Sub-picture Sizing In Video Coding

ABSTRACT

A video coding mechanism is disclosed. The mechanism includes receiving a bitstream comprising one or more sub-pictures partitioned from a picture such that each sub-picture includes a sub-picture width that is an integer multiple of a coding tree unit (CTU) size when the each sub-picture includes a right boundary that does not coincide with a right boundary of the picture. The bitstream is parsed to obtain the one or more sub-pictures. The one or more sub-pictures are decoded to create a video sequence. The video sequence is forwarded for display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 17/370,913 filed on Jul. 8, 2021, which is a continuation ofInternational Application No. PCT/US2020/012910, filed Jan. 9, 2020 byYe-Kui Wang, et. al., and titled “Sub-picture Sizing In Video Coding,”which claims the benefit of U.S. Provisional Patent Application No.62/790,207, filed Jan. 9, 2019 by Ye-Kui Wang, et. al., and titled“Sub-Pictures in Video Coding,” which are hereby incorporated byreference.

TECHNICAL FIELD

The present disclosure is generally related to video coding, and isspecifically related to sub-picture management in video coding.

BACKGROUND

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in image qualityare desirable.

SUMMARY

In an embodiment, the disclosure includes a method implemented in adecoder, the method comprising: receiving, by a receiver of the decoder,a bitstream comprising one or more sub-pictures partitioned from apicture such that a first sub-picture comprises a sub-picture width thatincludes an incomplete coding tree unit (CTU) when the first sub-pictureincludes a right boundary that coincides with the right boundary of thepicture; parsing, by a processor of the decoder, the bitstream to obtainthe one or more sub-pictures; decoding, by the processor, the one ormore sub-pictures to create a video sequence; and forwarding, by theprocessor, the video sequence for display. Some video systems may limitsub-pictures to include heights and widths that are multiples of CTUsize. However, may pictures include heights and widths that are notmultiples of CTU size. Accordingly, the sub-picture size constraintsprevent sub-pictures from operating correctly with many picture layouts.In the disclosed examples, sub-picture widths and sub-picture heightsare constrained to be multiples of CTU size. However, these constraintsare removed when a sub-picture is positioned at the right boundary ofthe picture or the bottom boundary of the picture, respectively. Byallowing the bottom and right sub-pictures to include heights andwidths, respectively, that are not multiples of CTU size, sub-picturesmay be used with any picture without causing decoding errors. Thisresults in increasing encoder and decoder functionality. Further, theincreased functionality allows an encoder to code pictures moreefficiently, which reduces the usage of network resources, memoryresources, and/or processing resources at the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a second sub-picture comprises asub-picture height that includes an integer number of complete CTUs whenthe second sub-picture includes a bottom boundary that does not coincidewith a bottom boundary of the picture.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a third sub-picture comprises a sub-picturewidth that includes an integer number of complete CTUs when the thirdsub-picture includes a right boundary that does not coincide with aright boundary of the picture.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a fourth sub-picture comprises asub-picture height that includes an incomplete CTU when the fourthsub-picture includes a bottom boundary that coincides with the bottomboundary of the picture.

In an embodiment, the disclosure includes a method implemented in adecoder, the method comprising: receiving, by a receiver of the decoder,a bitstream comprising one or more sub-pictures partitioned from apicture such that each sub-picture includes a sub-picture width that isan integer multiple of a coding tree unit (CTU) size when the eachsub-picture includes a right boundary that does not coincide with aright boundary of the picture; parsing, by a processor of the decoder,the bitstream to obtain the one or more sub-pictures; decoding, by theprocessor, the one or more sub-pictures to create a video sequence; andforwarding, by the processor, the video sequence for display. Some videosystems may limit sub-pictures to include heights and widths that aremultiples of CTU size. However, may pictures include heights and widthsthat are not multiples of CTU size. Accordingly, the sub-picture sizeconstraints prevent sub-pictures from operating correctly with manypicture layouts. In the disclosed examples, sub-picture widths andsub-picture heights are constrained to be multiples of CTU size.However, these constraints are removed when a sub-picture is positionedat the right boundary of the picture or the bottom boundary of thepicture, respectively. By allowing the bottom and right sub-pictures toinclude heights and widths, respectively, that are not multiples of CTUsize, sub-pictures may be used with any picture without causing decodingerrors. This results in increasing encoder and decoder functionality.Further, the increased functionality allows an encoder to code picturesmore efficiently, which reduces the usage of network resources, memoryresources, and/or processing resources at the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein each sub-picture includes a sub-pictureheight that is an integer multiple of the CTU size when the eachsub-picture includes a bottom boundary that does not coincide with abottom boundary of the picture.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein at least one of the sub-pictures includes asub-picture width that is not an integer multiple of the CTU size whenthe each sub-picture includes a right boundary that coincides with theright boundary of the picture.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein at least one of the sub-pictures includes asub-picture height that is not an integer multiple of the CTU size whenthe each sub-picture includes a bottom boundary that coincides with thebottom boundary of the picture.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the picture includes a picture width thatis not an integer multiple of the CTU size.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the picture includes a picture height thatis not an integer multiple of the CTU size.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the CTU size is measured in units of lumasamples.

In an embodiment, the disclosure includes a method implemented in anencoder, the method comprising: partitioning, by a processor of theencoder, a picture into a plurality of sub-pictures such that eachsub-picture includes a sub-picture width that is an integer multiple ofa CTU size when the each sub-picture includes a right boundary that doesnot coincide with a right boundary of the picture; encoding, by theprocessor, one or more of the sub-pictures into a bitstream; andstoring, in a memory of the encoder, the bitstream for communicationtoward a decoder. Some video systems may limit sub-pictures to includeheights and widths that are multiples of CTU size. However, may picturesinclude heights and widths that are not multiples of CTU size.Accordingly, the sub-picture size constraints prevent sub-pictures fromoperating correctly with many picture layouts. In the disclosedexamples, sub-picture widths and sub-picture heights are constrained tobe multiples of CTU size. However, these constraints are removed when asub-picture is positioned at the right boundary of the picture or thebottom boundary of the picture, respectively. By allowing the bottom andright sub-pictures to include heights and widths, respectively, that arenot multiples of CTU size, sub-pictures may be used with any picturewithout causing decoding errors. This results in increasing encoder anddecoder functionality. Further, the increased functionality allows anencoder to code pictures more efficiently, which reduces the usage ofnetwork resources, memory resources, and/or processing resources at theencoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein each sub-picture includes a sub-pictureheight that is an integer multiple of the CTU size when the eachsub-picture includes a bottom boundary that does not coincide with abottom boundary of the picture.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein at least one of the sub-pictures includes asub-picture width that is not an integer multiple of the CTU size whenthe each sub-picture includes a right boundary that coincides with theright boundary of the picture.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein at least one of the sub-pictures includes asub-picture height that is not an integer multiple of the CTU size whenthe each sub-picture includes a bottom boundary that coincides with thebottom boundary of the picture.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the picture includes a picture width thatis not an integer multiple of the CTU size.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the picture includes a picture height thatis not an integer multiple of the CTU size.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the CTU size is measured in units of lumasamples.

In an embodiment, the disclosure includes a video coding devicecomprising: a processor, a memory, a receiver coupled to the processor,and a transmitter coupled to the processor, the processor, memory,receiver, and transmitter configured to perform the method of any of thepreceding aspects.

In an embodiment, the disclosure includes a non-transitory computerreadable medium comprising a computer program product for use by a videocoding device, the computer program product comprising computerexecutable instructions stored on the non-transitory computer readablemedium such that when executed by a processor cause the video codingdevice to perform the method of any of the preceding aspects.

In an embodiment, the disclosure includes a decoder comprising: areceiving means for receiving a bitstream comprising one or moresub-pictures partitioned from a picture such that each sub-pictureincludes a sub-picture width that is an integer multiple of a CTU sizewhen the each sub-picture includes a right boundary that does notcoincide with a right border of the picture; a parsing means for parsingthe bitstream to obtain the one or more sub-pictures; a decoding meansfor decoding the one or more sub-pictures to create a video sequence;and a forwarding means for forwarding the video sequence for display.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the decoder is further configured toperform the method of any of the preceding aspects.

In an embodiment, the disclosure includes an encoder comprising: apartitioning means for partitioning a picture into a plurality ofsub-pictures such that each sub-picture includes a sub-picture widththat is an integer multiple of a CTU size when the each sub-pictureincludes a right boundary that does not coincide with a right boundaryof the picture; an encoding means for encoding one or more of thesub-pictures into a bitstream; and a storing means for storing thebitstream for communication toward a decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the encoder is further configured toperform the method of any of the preceding aspects.

For the purpose of clarity, any one of the foregoing embodiments may becombined with any one or more of the other foregoing embodiments tocreate a new embodiment within the scope of the present disclosure.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a flowchart of an example method of coding a video signal.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system for video coding.

FIG. 3 is a schematic diagram illustrating an example video encoder.

FIG. 4 is a schematic diagram illustrating an example video decoder.

FIG. 5 is a schematic diagram illustrating an example bitstream andsub-bitstream extracted from the bitstream.

FIG. 6 is a schematic diagram illustrating an example picturepartitioned into sub-pictures.

FIG. 7 is a schematic diagram illustrating an example mechanism forrelating slices to a sub-picture layout.

FIG. 8 is a schematic diagram illustrating another example picturepartitioned into sub-pictures.

FIG. 9 is a schematic diagram of an example video coding device.

FIG. 10 is a flowchart of an example method of encoding a bitstream ofsub-pictures with adaptive size constraints.

FIG. 11 is a flowchart of an example method of decoding a bitstream ofsub-pictures with adaptive size constraints.

FIG. 12 is a schematic diagram of an example system for signaling abitstream of sub-pictures with adaptive size constraints.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Various acronyms are employed herein, such as coding tree block (CTB),coding tree unit (CTU), coding unit (CU), coded video sequence (CVS),Joint Video Experts Team (JVET), motion constrained tile set (MCTS),maximum transfer unit (MTU), network abstraction layer (NAL), pictureorder count (POC), raw byte sequence payload (RBSP), sequence parameterset (SPS), versatile video coding (VVC), and working draft (WD).

Many video compression techniques can be employed to reduce the size ofvideo files with minimal loss of data. For example, video compressiontechniques can include performing spatial (e.g., intra-picture)prediction and/or temporal (e.g., inter-picture) prediction to reduce orremove data redundancy in video sequences. For block-based video coding,a video slice (e.g., a video picture or a portion of a video picture)may be partitioned into video blocks, which may also be referred to astreeblocks, coding tree blocks (CTBs), coding tree units (CTUs), codingunits (CUs), and/or coding nodes. Video blocks in an intra-coded (I)slice of a picture are coded using spatial prediction with respect toreference samples in neighboring blocks in the same picture. Videoblocks in an inter-coded unidirectional prediction (P) or bidirectionalprediction (B) slice of a picture may be coded by employing spatialprediction with respect to reference samples in neighboring blocks inthe same picture or temporal prediction with respect to referencesamples in other reference pictures. Pictures may be referred to asframes and/or images, and reference pictures may be referred to asreference frames and/or reference images. Spatial or temporal predictionresults in a predictive block representing an image block. Residual datarepresents pixel differences between the original image block and thepredictive block. Accordingly, an inter-coded block is encoded accordingto a motion vector that points to a block of reference samples formingthe predictive block and the residual data indicating the differencebetween the coded block and the predictive block. An intra-coded blockis encoded according to an intra-coding mode and the residual data. Forfurther compression, the residual data may be transformed from the pixeldomain to a transform domain. These result in residual transformcoefficients, which may be quantized. The quantized transformcoefficients may initially be arranged in a two-dimensional array. Thequantized transform coefficients may be scanned in order to produce aone-dimensional vector of transform coefficients. Entropy coding may beapplied to achieve even more compression. Such video compressiontechniques are discussed in greater detail below.

To ensure an encoded video can be accurately decoded, video is encodedand decoded according to corresponding video coding standards. Videocoding standards include International Telecommunication Union (ITU)Standardization Sector (ITU-T) H.261, International Organization forStandardization/International Electrotechnical Commission (ISO/IEC)Motion Picture Experts Group (MPEG)-1 Part 2, ITU-T H.262 or ISO/IECMPEG-2 Part 2, ITU-T H.263, ISO/IEC MPEG-4 Part 2, Advanced Video Coding(AVC), also known as ITU-T H.264 or ISO/IEC MPEG-4 Part 10, and HighEfficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part2. AVC includes extensions such as Scalable Video Coding (SVC),Multiview Video Coding (MVC) and Multiview Video Coding plus Depth(MVC+D), and three dimensional (3D) AVC (3D-AVC). HEVC includesextensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and3D HEVC (3D-HEVC). The joint video experts team (JVET) of ITU-T andISO/IEC has begun developing a video coding standard referred to asVersatile Video Coding (VVC). VVC is included in a Working Draft (WD),which includes JVET-L1001-v9.

In order to code a video image, the image is first partitioned, and thepartitions are coded into a bitstream. Various picture partitioningschemes are available. For example, an image can be partitioned intoregular slices, dependent slices, tiles, and/or according to WavefrontParallel Processing (WPP). For simplicity, HEVC restricts encoders sothat only regular slices, dependent slices, tiles, WPP, and combinationsthereof can be used when partitioning a slice into groups of CTBs forvideo coding. Such partitioning can be applied to support MaximumTransfer Unit (MTU) size matching, parallel processing, and reducedend-to-end delay. MTU denotes the maximum amount of data that can betransmitted in a single packet. If a packet payload is in excess of theMTU, that payload is split into two packets through a process calledfragmentation.

A regular slice, also referred to simply as a slice, is a partitionedportion of an image that can be reconstructed independently from otherregular slices within the same picture, notwithstanding someinterdependencies due to loop filtering operations. Each regular sliceis encapsulated in its own Network Abstraction Layer (NAL) unit fortransmission. Further, in-picture prediction (intra sample prediction,motion information prediction, coding mode prediction) and entropycoding dependency across slice boundaries may be disabled to supportindependent reconstruction. Such independent reconstruction supportsparallelization. For example, regular slice based parallelizationemploys minimal inter-processor or inter-core communication. However, aseach regular slice is independent, each slice is associated with aseparate slice header. The use of regular slices can incur a substantialcoding overhead due to the bit cost of the slice header for each sliceand due to the lack of prediction across the slice boundaries. Further,regular slices may be employed to support matching for MTU sizerequirements. Specifically, as a regular slice is encapsulated in aseparate NAL unit and can be independently coded, each regular sliceshould be smaller than the MTU in MTU schemes to avoid breaking theslice into multiple packets. As such, the goal of parallelization andthe goal of MTU size matching may place contradicting demands to a slicelayout in a picture.

Dependent slices are similar to regular slices, but have shortened sliceheaders and allow partitioning of the image treeblock boundaries withoutbreaking in-picture prediction. Accordingly, dependent slices allow aregular slice to be fragmented into multiple NAL units, which providesreduced end-to-end delay by allowing a part of a regular slice to besent out before the encoding of the entire regular slice is complete.

A tile is a partitioned portion of an image created by horizontal andvertical boundaries that create columns and rows of tiles. Tiles may becoded in raster scan order (right to left and top to bottom). The scanorder of CTBs is local within a tile. Accordingly, CTBs in a first tileare coded in raster scan order, before proceeding to the CTBs in thenext tile. Similar to regular slices, tiles break in-picture predictiondependencies as well as entropy decoding dependencies. However, tilesmay not be included into individual NAL units, and hence tiles may notbe used for MTU size matching. Each tile can be processed by oneprocessor/core, and the inter-processor/inter-core communicationemployed for in-picture prediction between processing units decodingneighboring tiles may be limited to conveying a shared slice header(when adjacent tiles are in the same slice), and performing loopfiltering related sharing of reconstructed samples and metadata. Whenmore than one tile is included in a slice, the entry point byte offsetfor each tile other than the first entry point offset in the slice maybe signaled in the slice header. For each slice and tile, at least oneof the following conditions should be fulfilled: 1) all coded treeblocksin a slice belong to the same tile; and 2) all coded treeblocks in atile belong to the same slice.

In WPP, the image is partitioned into single rows of CTBs. Entropydecoding and prediction mechanisms may use data from CTBs in other rows.Parallel processing is made possible through parallel decoding of CTBrows. For example, a current row may be decoded in parallel with apreceding row. However, decoding of the current row is delayed from thedecoding process of the preceding rows by two CTBs. This delay ensuresthat data related to the CTB above and the CTB above and to the right ofthe current CTB in the current row is available before the current CTBis coded. This approach appears as a wavefront when representedgraphically. This staggered start allows for parallelization with up toas many processors/cores as the image contains CTB rows. Becausein-picture prediction between neighboring treeblock rows within apicture is permitted, the inter-processor/inter-core communication toenable in-picture prediction can be substantial. The WPP partitioningdoes consider NAL unit sizes. Hence, WPP does not support MTU sizematching. However, regular slices can be used in conjunction with WPP,with certain coding overhead, to implement MTU size matching as desired.

Tiles may also include motion constrained tile sets. A motionconstrained tile set (MCTS) is a tile set designed such that associatedmotion vectors are restricted to point to full-sample locations insidethe MCTS and to fractional-sample locations that require onlyfull-sample locations inside the MCTS for interpolation. Further, theusage of motion vector candidates for temporal motion vector predictionderived from blocks outside the MCTS is disallowed. This way, each MCTSmay be independently decoded without the existence of tiles not includedin the MCTS. Temporal MCTSs supplemental enhancement information (SEI)messages may be used to indicate the existence of MCTSs in the bitstreamand signal the MCTSs. The MCTSs SEI message provides supplementalinformation that can be used in the MCTS sub-bitstream extraction(specified as part of the semantics of the SEI message) to generate aconforming bitstream for an MCTS set. The information includes a numberof extraction information sets, each defining a number of MCTS sets andcontaining raw bytes sequence payload (RB SP) bytes of the replacementvideo parameter sets (VPS s), sequence parameter sets (SPSs), andpicture parameter sets (PPSs) to be used during the MCTS sub-bitstreamextraction process. When extracting a sub-bitstream according to theMCTS sub-bitstream extraction process, parameter sets (VPSs, SPSs, andPPSs) may be rewritten or replaced, and slice headers may updatedbecause one or all of the slice address related syntax elements(including first_slice_segment_in_pic_flag and slice_segment_address)may employ different values in the extracted sub-bitstream.

A picture may also be partitioned into one or more sub-pictures. Asub-picture is a rectangular set of tile groups/slices that begins witha tile group that has a tile_group_address equal to zero. Eachsub-picture may refer to a separate PPS and may therefore have aseparate tile partitioning. Sub-pictures may be treated like pictures inthe decoding process. The reference sub-pictures for decoding a currentsub-picture are generated by extracting the area collocated with thecurrent sub-picture from the reference pictures in the decoded picturebuffer. The extracted area is treated as a decoded sub-picture.Inter-prediction may take place between sub-pictures of the same sizeand the same location within the picture. A tile group, also known as aslice, is a sequence of related tiles in a picture or a sub-picture.Several items can be derived to determine a location of the sub-picturein a picture. For example, each current sub-picture may be positioned inthe next unoccupied location in CTU raster scan order within a picturethat is large enough to contain the current sub-picture within thepicture boundaries.

Further, picture partitioning may be based on picture level tiles andsequence level tiles. Sequence level tiles may include the functionalityof MCTS, and may be implemented as sub-pictures. For example, a picturelevel tile may be defined as a rectangular region of coding tree blockswithin a particular tile column and a particular tile row in a picture.A sequence level tile may be defined as a set of rectangular regions ofcoding tree blocks included in different frames where each rectangularregion further comprises one or more picture-level tiles and the set ofrectangular regions of coding tree blocks are independently decodablefrom any other set of similar rectangular regions. A sequence level tilegroup set (STGPS) is a group of such sequence level tiles. The STGPS maybe signaled in a non-video coding layer (VCL) NAL unit with anassociated identifier (ID) in the NAL unit header.

The preceding sub-picture based partitioning scheme may be associatedwith certain problems. For example, when sub-pictures are enabled tilingwithin sub-pictures (partitioning of sub-pictures into tiles) can beused to support parallel processing. Tile partitioning of sub-picturesfor parallel processing purposes can change from picture to picture(e.g., for parallel processing load balancing purposes), and thereforemay be managed at the picture level (e.g., in the PPS). However,sub-picture partitioning (partitioning of pictures into sub-pictures)may be employed to support region of interest (ROI) and sub-picturebased picture access. In such a case, signaling of sub-pictures or MCTSin the PPS is not efficient.

In another example, when any sub-picture in a picture is coded as atemporal motion constrained sub-picture, all sub-pictures in the picturemay be coded as temporal motion-constrained sub-pictures. Such picturepartitioning may be limiting. For example, coding a sub-picture as atemporal motion-constrained sub-picture may reduce coding efficiency inexchange for additional functionality. However, in region ofinterest-based applications, usually only one or a few of thesub-pictures use temporal motion-constrained sub-picture basedfunctionality. Hence, the remaining sub-pictures suffer from reducedcoding efficiency without providing any practical benefit.

In another example, the syntax elements for specifying the size of asub-picture may be specified in units of luma CTU sizes. Accordingly,both sub-picture width and height should be an integer multiple ofCtbSizeY. This mechanism of specifying sub-picture width and height mayresult in various issues. For example, sub-picture partitioning is onlyapplicable to pictures with picture width and/or picture height that arean integer multiple of CtbSizeY. This renders sub-picture partitioningas unavailable for pictures that contain dimensions that are not integermultiples of CTbSizeY. If sub-picture partitioning were applied topicture width and/or height when the picture dimension is not an integermultiple of CtbSizeY, the derivation of sub-picture width and/orsub-picture height in luma samples for the right most sub-picture andbottom most sub-picture would be incorrect. Such incorrect derivationwould cause erroneous results in some coding tools.

In another example, the location of a sub-picture in a picture may notbe signaled. The location is instead derived using the following rule.The current sub-picture is positioned in the next such unoccupiedlocation in CTU raster scan order within a picture that is large enoughto contain the sub-picture within the picture boundaries. Derivingsub-picture locations in such a way may cause errors in some cases. Forexample, if a sub-picture is lost in transmission, then the locations ofother sub-pictures are derived incorrectly and the decoded samples areplaced at erroneous locations. The same problem applies when thesub-pictures arrive in the wrong order.

In another example, decoding a sub-picture may require extraction ofco-located sub-pictures in reference pictures. This may imposeadditional complexity and resulting burdens in terms of processor andmemory resource usage.

In another example, when a sub-picture is designated as a temporalmotion constrained sub-picture, loop filters that traverse thesub-picture boundary are disabled. This occurs regardless of whetherloop filters that traverse tile boundaries are enabled. Such aconstraint may be too restrictive and may result in visual artefacts forvideo pictures employing multiple of sub-pictures.

In another example, the relationship between the SPS, STGPS, PPS andtile group headers is as follows. The STGPS refers to the SPS, the PPSrefers to the STGPS, and the tile group headers/slice headers refer tothe PPS. However, the STGPS and the PPS should be orthogonal rather thanthe PPS referring to the STGPS. The preceding arrangement may alsodisallow all tile groups of the same picture from referring to the samePPS.

In another example, each STGPS may contain IDs for four sides of asub-picture. Such IDs are used to identify sub-pictures that share thesame border so that their relative spatial relationship can be defined.However, such information may not be sufficient to derive the positionand size information for a sequence level tile group set in some cases.In other cases signaling, the position and size information may beredundant.

In another example, an STGPS ID may be signaled in a NAL unit header ofa VCL NAL unit using eight bits. This may assist with sub-pictureextraction. Such signaling may unnecessarily increase the length of theNAL unit header. Another issue is that unless the sequence level tilegroup sets are constrained to prevent overlaps, one tile group may beassociated with multiple sequence level tile group sets.

Disclosed herein are various mechanisms to address one or more of theabovementioned problems. In a first example, the layout information forsub-pictures is included in an SPS instead of a PPS. Sub-picture layoutinformation includes sub-picture location and sub-picture size.Sub-picture location is an offset between the top left sample of thesub-picture and the top left sample of the picture. Sub-picture size isthe height and width of the sub-picture as measured in luma samples. Asnoted above, some systems include tiling information in the PPS as tilesmay change from picture to picture. However, sub-pictures may be used tosupport ROI applications and sub-picture based access. These functionsdo not change on a per picture basis. Further, a video sequence mayinclude a single SPS (or one per video segment), and may include as manyas one PPS per picture. Placing layout information for sub-pictures inthe SPS ensures that the layout is only signaled once for asequence/segment rather than redundantly signaled for each PPS.Accordingly, signaling sub-picture layout in the SPS increases codingefficiency and hence reduces the usage of network resources, memoryresources, and/or processing resources at the encoder and the decoder.Also, some systems have the sub-picture information derived by thedecoder. Signaling the sub-picture information reduces the possibilityof error in case of lost packets and supports additional functionalityin terms of extracting sub-pictures. Accordingly, signaling sub-picturelayout in the SPS improves the functionality of an encoder and/ordecoder.

In a second example, sub-picture widths and sub-picture heights areconstrained to be multiples of CTU size. However, these constraints areremoved when a sub-picture is positioned at the right border of thepicture or the bottom border of the picture, respectively. As notedabove, some video systems may limit sub-pictures to include heights andwidths that are multiples of CTU size. This prevents sub-pictures fromoperating correctly with many picture layouts. By allowing the bottomand right sub-pictures to include heights and widths, respectively, thatare not be multiples of CTU size, sub-pictures may be used with anypicture without causing decoding errors. This results in increasingencoder and decoder functionality. Further, the increased functionalityallows an encoder to code pictures more efficiently, which reduces theusage of network resources, memory resources, and/or processingresources at the encoder and the decoder.

In a third example, sub-pictures are constrained to cover a picturewithout gap or overlap. As noted above, some video coding systems allowsub-pictures to include gaps and overlaps. This creates the potentialfor tile groups/slices to be associated with multiple sub-pictures. Ifthis is allowed at the encoder, decoders must be built to support such acoding scheme even when the decoding scheme is rarely used. Bydisallowing sub-picture gaps and overlaps, the complexity of the decodercan be decreased as the decoder is not required to account for potentialgaps and overlaps when determining sub-picture sizes and locations.Further, disallowing sub-picture gaps and overlaps reduces complexity ofrate distortion optimization (RDO) processes at the encoder as theencoder can omit considering gap and overlap cases when selecting anencoding for a video sequence. Accordingly, avoiding gaps and overlapsmay reduce the usage of memory resources and/or processing resources atthe encoder and the decoder.

In a fourth example, a flag can be signaled in the SPS to indicate whena sub-picture is a temporal motion constrained sub-picture. As notedabove, some systems may collectively set all sub-pictures to be temporalmotion constrained sub-pictures or completely disallow usage of temporalmotion constrained sub-pictures. Such temporal motion constrainedsub-pictures provide independent extraction functionality at the cost ofdecreased coding efficiency. However, in region of interest-basedapplications, the region of interest should be coded for independentextraction while the regions outside of the region of interest do notneed such functionality. Hence, the remaining sub-pictures suffer fromreduced coding efficiency without providing any practical benefit.Accordingly, the flag allows for a mixture of temporal motionconstrained sub-pictures that provide independent extractionfunctionality and non-motion constrained sub-pictures for increasedcoding efficiency when independent extraction is not desired. Hence, theflag allows for increased functionality and/or increased codingefficiency, which reduces the usage of network resources, memoryresources, and/or processing resources at the encoder and the decoder.

In a fifth example, a complete set of sub-picture IDs are signaled inthe SPS, and slice headers include a sub-picture ID indicating thesub-picture that contains the corresponding slices. As noted above, somesystems signal sub-picture positions relative to other sub-pictures.This causes a problem if sub-pictures are lost or are separatelyextracted. By designating each sub-picture by an ID, the sub-picturescan be positioned and sized without reference to other sub-pictures.This in turn supports error correction as well as applications that onlyextract some of the sub-pictures and avoid transmitting othersub-pictures. A complete list of all sub-picture IDs can be sent in theSPS along with relevant sizing information. Each slice header maycontain a sub-picture ID indicating the sub-picture that includes thecorresponding slice. In this way, sub-pictures and corresponding slicescan be extracted and positioned without reference to other sub-pictures.Hence, the sub-picture IDs support increased functionality and/orincreased coding efficiency, which reduces the usage of networkresources, memory resources, and/or processing resources at the encoderand the decoder.

In a sixth example, levels are signaled for each sub-picture. In somevideo coding systems levels are signaled for pictures. A level indicateshardware resources needed to decode the picture. As noted above,different sub-pictures may have different functionality in some casesand hence may be treated differently during the coding process. As such,a picture based level may not be useful for decoding some sub-pictures.Hence, the present disclosure includes levels for each sub-picture. Inthis way, each sub-picture can be coded independently of othersub-pictures without unnecessarily overtaxing the decoder by settingdecoding requirements too high for sub-pictures coded according to lesscomplex mechanisms. The signaled sub-picture level information supportsincreased functionality and/or increased coding efficiency, whichreduces the usage of network resources, memory resources, and/orprocessing resources at the encoder and the decoder.

FIG. 1 is a flowchart of an example operating method 100 of coding avideo signal. Specifically, a video signal is encoded at an encoder. Theencoding process compresses the video signal by employing variousmechanisms to reduce the video file size. A smaller file size allows thecompressed video file to be transmitted toward a user, while reducingassociated bandwidth overhead. The decoder then decodes the compressedvideo file to reconstruct the original video signal for display to anend user. The decoding process generally mirrors the encoding process toallow the decoder to consistently reconstruct the video signal.

At step 101, the video signal is input into the encoder. For example,the video signal may be an uncompressed video file stored in memory. Asanother example, the video file may be captured by a video capturedevice, such as a video camera, and encoded to support live streaming ofthe video. The video file may include both an audio component and avideo component. The video component contains a series of image framesthat, when viewed in a sequence, gives the visual impression of motion.The frames contain pixels that are expressed in terms of light, referredto herein as luma components (or luma samples), and color, which isreferred to as chroma components (or color samples). In some examples,the frames may also contain depth values to support three dimensionalviewing.

At step 103, the video is partitioned into blocks. Partitioning includessubdividing the pixels in each frame into square and/or rectangularblocks for compression. For example, in High Efficiency Video Coding(HEVC) (also known as H.265 and MPEG-H Part 2) the frame can first bedivided into coding tree units (CTUs), which are blocks of a predefinedsize (e.g., sixty-four pixels by sixty-four pixels). The CTUs containboth luma and chroma samples. Coding trees may be employed to divide theCTUs into blocks and then recursively subdivide the blocks untilconfigurations are achieved that support further encoding. For example,luma components of a frame may be subdivided until the individual blockscontain relatively homogenous lighting values. Further, chromacomponents of a frame may be subdivided until the individual blockscontain relatively homogenous color values. Accordingly, partitioningmechanisms vary depending on the content of the video frames.

At step 105, various compression mechanisms are employed to compress theimage blocks partitioned at step 103. For example, inter-predictionand/or intra-prediction may be employed. Inter-prediction is designed totake advantage of the fact that objects in a common scene tend to appearin successive frames. Accordingly, a block depicting an object in areference frame need not be repeatedly described in adjacent frames.Specifically, an object, such as a table, may remain in a constantposition over multiple frames. Hence the table is described once andadjacent frames can refer back to the reference frame. Pattern matchingmechanisms may be employed to match objects over multiple frames.Further, moving objects may be represented across multiple frames, forexample due to object movement or camera movement. As a particularexample, a video may show an automobile that moves across the screenover multiple frames. Motion vectors can be employed to describe suchmovement. A motion vector is a two-dimensional vector that provides anoffset from the coordinates of an object in a frame to the coordinatesof the object in a reference frame. As such, inter-prediction can encodean image block in a current frame as a set of motion vectors indicatingan offset from a corresponding block in a reference frame.

Intra-prediction encodes blocks in a common frame. Intra-predictiontakes advantage of the fact that luma and chroma components tend tocluster in a frame. For example, a patch of green in a portion of a treetends to be positioned adjacent to similar patches of green.Intra-prediction employs multiple directional prediction modes (e.g.,thirty-three in HEVC), a planar mode, and a direct current (DC) mode.The directional modes indicate that a current block is similar/the sameas samples of a neighbor block in a corresponding direction. Planar modeindicates that a series of blocks along a row/column (e.g., a plane) canbe interpolated based on neighbor blocks at the edges of the row. Planarmode, in effect, indicates a smooth transition of light/color across arow/column by employing a relatively constant slope in changing values.DC mode is employed for boundary smoothing and indicates that a block issimilar/the same as an average value associated with samples of all theneighbor blocks associated with the angular directions of thedirectional prediction modes. Accordingly, intra-prediction blocks canrepresent image blocks as various relational prediction mode valuesinstead of the actual values. Further, inter-prediction blocks canrepresent image blocks as motion vector values instead of the actualvalues. In either case, the prediction blocks may not exactly representthe image blocks in some cases. Any differences are stored in residualblocks. Transforms may be applied to the residual blocks to furthercompress the file.

At step 107, various filtering techniques may be applied. In HEVC, thefilters are applied according to an in-loop filtering scheme. The blockbased prediction discussed above may result in the creation of blockyimages at the decoder. Further, the block based prediction scheme mayencode a block and then reconstruct the encoded block for later use as areference block. The in-loop filtering scheme iteratively applies noisesuppression filters, de-blocking filters, adaptive loop filters, andsample adaptive offset (SAO) filters to the blocks/frames. These filtersmitigate such blocking artifacts so that the encoded file can beaccurately reconstructed. Further, these filters mitigate artifacts inthe reconstructed reference blocks so that artifacts are less likely tocreate additional artifacts in subsequent blocks that are encoded basedon the reconstructed reference blocks.

Once the video signal has been partitioned, compressed, and filtered,the resulting data is encoded in a bitstream at step 109. The bitstreamincludes the data discussed above as well as any signaling data desiredto support proper video signal reconstruction at the decoder. Forexample, such data may include partition data, prediction data, residualblocks, and various flags providing coding instructions to the decoder.The bitstream may be stored in memory for transmission toward a decoderupon request. The bitstream may also be broadcast and/or multicasttoward a plurality of decoders. The creation of the bitstream is aniterative process. Accordingly, steps 101, 103, 105, 107, and 109 mayoccur continuously and/or simultaneously over many frames and blocks.The order shown in FIG. 1 is presented for clarity and ease ofdiscussion, and is not intended to limit the video coding process to aparticular order.

The decoder receives the bitstream and begins the decoding process atstep 111. Specifically, the decoder employs an entropy decoding schemeto convert the bitstream into corresponding syntax and video data. Thedecoder employs the syntax data from the bitstream to determine thepartitions for the frames at step 111. The partitioning should match theresults of block partitioning at step 103. Entropy encoding/decoding asemployed in step 111 is now described. The encoder makes many choicesduring the compression process, such as selecting block partitioningschemes from several possible choices based on the spatial positioningof values in the input image(s). Signaling the exact choices may employa large number of bins. As used herein, a bin is a binary value that istreated as a variable (e.g., a bit value that may vary depending oncontext). Entropy coding allows the encoder to discard any options thatare clearly not viable for a particular case, leaving a set of allowableoptions. Each allowable option is then assigned a code word. The lengthof the code words is based on the number of allowable options (e.g., onebin for two options, two bins for three to four options, etc.) Theencoder then encodes the code word for the selected option. This schemereduces the size of the code words as the code words are as big asdesired to uniquely indicate a selection from a small sub-set ofallowable options as opposed to uniquely indicating the selection from apotentially large set of all possible options. The decoder then decodesthe selection by determining the set of allowable options in a similarmanner to the encoder. By determining the set of allowable options, thedecoder can read the code word and determine the selection made by theencoder.

At step 113, the decoder performs block decoding. Specifically, thedecoder employs reverse transforms to generate residual blocks. Then thedecoder employs the residual blocks and corresponding prediction blocksto reconstruct the image blocks according to the partitioning. Theprediction blocks may include both intra-prediction blocks andinter-prediction blocks as generated at the encoder at step 105. Thereconstructed image blocks are then positioned into frames of areconstructed video signal according to the partitioning data determinedat step 111. Syntax for step 113 may also be signaled in the bitstreamvia entropy coding as discussed above.

At step 115, filtering is performed on the frames of the reconstructedvideo signal in a manner similar to step 107 at the encoder. Forexample, noise suppression filters, de-blocking filters, adaptive loopfilters, and SAO filters may be applied to the frames to remove blockingartifacts. Once the frames are filtered, the video signal can be outputto a display at step 117 for viewing by an end user.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system 200 for video coding. Specifically, codec system 200 providesfunctionality to support the implementation of operating method 100.Codec system 200 is generalized to depict components employed in both anencoder and a decoder. Codec system 200 receives and partitions a videosignal as discussed with respect to steps 101 and 103 in operatingmethod 100, which results in a partitioned video signal 201. Codecsystem 200 then compresses the partitioned video signal 201 into a codedbitstream when acting as an encoder as discussed with respect to steps105, 107, and 109 in method 100. When acting as a decoder codec system200 generates an output video signal from the bitstream as discussedwith respect to steps 111, 113, 115, and 117 in operating method 100.The codec system 200 includes a general coder control component 211, atransform scaling and quantization component 213, an intra-pictureestimation component 215, an intra-picture prediction component 217, amotion compensation component 219, a motion estimation component 221, ascaling and inverse transform component 229, a filter control analysiscomponent 227, an in-loop filters component 225, a decoded picturebuffer component 223, and a header formatting and context adaptivebinary arithmetic coding (CABAC) component 231. Such components arecoupled as shown. In FIG. 2 , black lines indicate movement of data tobe encoded/decoded while dashed lines indicate movement of control datathat controls the operation of other components. The components of codecsystem 200 may all be present in the encoder. The decoder may include asubset of the components of codec system 200. For example, the decodermay include the intra-picture prediction component 217, the motioncompensation component 219, the scaling and inverse transform component229, the in-loop filters component 225, and the decoded picture buffercomponent 223. These components are now described.

The partitioned video signal 201 is a captured video sequence that hasbeen partitioned into blocks of pixels by a coding tree. A coding treeemploys various split modes to subdivide a block of pixels into smallerblocks of pixels. These blocks can then be further subdivided intosmaller blocks. The blocks may be referred to as nodes on the codingtree. Larger parent nodes are split into smaller child nodes. The numberof times a node is subdivided is referred to as the depth of thenode/coding tree. The divided blocks can be included in coding units(CUs) in some cases. For example, a CU can be a sub-portion of a CTUthat contains a luma block, red difference chroma (Cr) block(s), and ablue difference chroma (Cb) block(s) along with corresponding syntaxinstructions for the CU. The split modes may include a binary tree (BT),triple tree (TT), and a quad tree (QT) employed to partition a node intotwo, three, or four child nodes, respectively, of varying shapesdepending on the split modes employed. The partitioned video signal 201is forwarded to the general coder control component 211, the transformscaling and quantization component 213, the intra-picture estimationcomponent 215, the filter control analysis component 227, and the motionestimation component 221 for compression.

The general coder control component 211 is configured to make decisionsrelated to coding of the images of the video sequence into the bitstreamaccording to application constraints. For example, the general codercontrol component 211 manages optimization of bitrate/bitstream sizeversus reconstruction quality. Such decisions may be made based onstorage space/bandwidth availability and image resolution requests. Thegeneral coder control component 211 also manages buffer utilization inlight of transmission speed to mitigate buffer underrun and overrunissues. To manage these issues, the general coder control component 211manages partitioning, prediction, and filtering by the other components.For example, the general coder control component 211 may dynamicallyincrease compression complexity to increase resolution and increasebandwidth usage or decrease compression complexity to decreaseresolution and bandwidth usage. Hence, the general coder controlcomponent 211 controls the other components of codec system 200 tobalance video signal reconstruction quality with bit rate concerns. Thegeneral coder control component 211 creates control data, which controlsthe operation of the other components. The control data is alsoforwarded to the header formatting and CABAC component 231 to be encodedin the bitstream to signal parameters for decoding at the decoder.

The partitioned video signal 201 is also sent to the motion estimationcomponent 221 and the motion compensation component 219 forinter-prediction. A frame or slice of the partitioned video signal 201may be divided into multiple video blocks. Motion estimation component221 and the motion compensation component 219 perform inter-predictivecoding of the received video block relative to one or more blocks in oneor more reference frames to provide temporal prediction. Codec system200 may perform multiple coding passes, e.g., to select an appropriatecoding mode for each block of video data.

Motion estimation component 221 and motion compensation component 219may be highly integrated, but are illustrated separately for conceptualpurposes. Motion estimation, performed by motion estimation component221, is the process of generating motion vectors, which estimate motionfor video blocks. A motion vector, for example, may indicate thedisplacement of a coded object relative to a predictive block. Apredictive block is a block that is found to closely match the block tobe coded, in terms of pixel difference. A predictive block may also bereferred to as a reference block. Such pixel difference may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. HEVC employs several coded objectsincluding a CTU, coding tree blocks (CTBs), and CUs. For example, a CTUcan be divided into CTBs, which can then be divided into CBs forinclusion in CUs. A CU can be encoded as a prediction unit (PU)containing prediction data and/or a transform unit (TU) containingtransformed residual data for the CU. The motion estimation component221 generates motion vectors, PUs, and TUs by using a rate-distortionanalysis as part of a rate distortion optimization process. For example,the motion estimation component 221 may determine multiple referenceblocks, multiple motion vectors, etc. for a current block/frame, and mayselect the reference blocks, motion vectors, etc. having the bestrate-distortion characteristics. The best rate-distortioncharacteristics balance both quality of video reconstruction (e.g.,amount of data loss by compression) with coding efficiency (e.g., sizeof the final encoding).

In some examples, codec system 200 may calculate values for sub-integerpixel positions of reference pictures stored in decoded picture buffercomponent 223. For example, video codec system 200 may interpolatevalues of one-quarter pixel positions, one-eighth pixel positions, orother fractional pixel positions of the reference picture. Therefore,motion estimation component 221 may perform a motion search relative tothe full pixel positions and fractional pixel positions and output amotion vector with fractional pixel precision. The motion estimationcomponent 221 calculates a motion vector for a PU of a video block in aninter-coded slice by comparing the position of the PU to the position ofa predictive block of a reference picture. Motion estimation component221 outputs the calculated motion vector as motion data to headerformatting and CABAC component 231 for encoding and motion to the motioncompensation component 219.

Motion compensation, performed by motion compensation component 219, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation component 221. Again, motionestimation component 221 and motion compensation component 219 may befunctionally integrated, in some examples. Upon receiving the motionvector for the PU of the current video block, motion compensationcomponent 219 may locate the predictive block to which the motion vectorpoints. A residual video block is then formed by subtracting pixelvalues of the predictive block from the pixel values of the currentvideo block being coded, forming pixel difference values. In general,motion estimation component 221 performs motion estimation relative toluma components, and motion compensation component 219 uses motionvectors calculated based on the luma components for both chromacomponents and luma components. The predictive block and residual blockare forwarded to transform scaling and quantization component 213.

The partitioned video signal 201 is also sent to intra-pictureestimation component 215 and intra-picture prediction component 217. Aswith motion estimation component 221 and motion compensation component219, intra-picture estimation component 215 and intra-picture predictioncomponent 217 may be highly integrated, but are illustrated separatelyfor conceptual purposes. The intra-picture estimation component 215 andintra-picture prediction component 217 intra-predict a current blockrelative to blocks in a current frame, as an alternative to theinter-prediction performed by motion estimation component 221 and motioncompensation component 219 between frames, as described above. Inparticular, the intra-picture estimation component 215 determines anintra-prediction mode to use to encode a current block. In someexamples, intra-picture estimation component 215 selects an appropriateintra-prediction mode to encode a current block from multiple testedintra-prediction modes. The selected intra-prediction modes are thenforwarded to the header formatting and CABAC component 231 for encoding.

For example, the intra-picture estimation component 215 calculatesrate-distortion values using a rate-distortion analysis for the varioustested intra-prediction modes, and selects the intra-prediction modehaving the best rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original unencoded block thatwas encoded to produce the encoded block, as well as a bitrate (e.g., anumber of bits) used to produce the encoded block. The intra-pictureestimation component 215 calculates ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block. In addition,intra-picture estimation component 215 may be configured to code depthblocks of a depth map using a depth modeling mode (DMM) based onrate-distortion optimization (RDO).

The intra-picture prediction component 217 may generate a residual blockfrom the predictive block based on the selected intra-prediction modesdetermined by intra-picture estimation component 215 when implemented onan encoder or read the residual block from the bitstream whenimplemented on a decoder. The residual block includes the difference invalues between the predictive block and the original block, representedas a matrix. The residual block is then forwarded to the transformscaling and quantization component 213. The intra-picture estimationcomponent 215 and the intra-picture prediction component 217 may operateon both luma and chroma components.

The transform scaling and quantization component 213 is configured tofurther compress the residual block. The transform scaling andquantization component 213 applies a transform, such as a discretecosine transform (DCT), a discrete sine transform (DST), or aconceptually similar transform, to the residual block, producing a videoblock comprising residual transform coefficient values. Wavelettransforms, integer transforms, sub-band transforms or other types oftransforms could also be used. The transform may convert the residualinformation from a pixel value domain to a transform domain, such as afrequency domain. The transform scaling and quantization component 213is also configured to scale the transformed residual information, forexample based on frequency. Such scaling involves applying a scalefactor to the residual information so that different frequencyinformation is quantized at different granularities, which may affectfinal visual quality of the reconstructed video. The transform scalingand quantization component 213 is also configured to quantize thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, the transform scaling andquantization component 213 may then perform a scan of the matrixincluding the quantized transform coefficients. The quantized transformcoefficients are forwarded to the header formatting and CABAC component231 to be encoded in the bitstream.

The scaling and inverse transform component 229 applies a reverseoperation of the transform scaling and quantization component 213 tosupport motion estimation. The scaling and inverse transform component229 applies inverse scaling, transformation, and/or quantization toreconstruct the residual block in the pixel domain, e.g., for later useas a reference block which may become a predictive block for anothercurrent block. The motion estimation component 221 and/or motioncompensation component 219 may calculate a reference block by adding theresidual block back to a corresponding predictive block for use inmotion estimation of a later block/frame. Filters are applied to thereconstructed reference blocks to mitigate artifacts created duringscaling, quantization, and transform. Such artifacts could otherwisecause inaccurate prediction (and create additional artifacts) whensubsequent blocks are predicted.

The filter control analysis component 227 and the in-loop filterscomponent 225 apply the filters to the residual blocks and/or toreconstructed image blocks. For example, the transformed residual blockfrom the scaling and inverse transform component 229 may be combinedwith a corresponding prediction block from intra-picture predictioncomponent 217 and/or motion compensation component 219 to reconstructthe original image block. The filters may then be applied to thereconstructed image block. In some examples, the filters may instead beapplied to the residual blocks. As with other components in FIG. 2 , thefilter control analysis component 227 and the in-loop filters component225 are highly integrated and may be implemented together, but aredepicted separately for conceptual purposes. Filters applied to thereconstructed reference blocks are applied to particular spatial regionsand include multiple parameters to adjust how such filters are applied.The filter control analysis component 227 analyzes the reconstructedreference blocks to determine where such filters should be applied andsets corresponding parameters. Such data is forwarded to the headerformatting and CABAC component 231 as filter control data for encoding.The in-loop filters component 225 applies such filters based on thefilter control data. The filters may include a deblocking filter, anoise suppression filter, a SAO filter, and an adaptive loop filter.Such filters may be applied in the spatial/pixel domain (e.g., on areconstructed pixel block) or in the frequency domain, depending on theexample.

When operating as an encoder, the filtered reconstructed image block,residual block, and/or prediction block are stored in the decodedpicture buffer component 223 for later use in motion estimation asdiscussed above. When operating as a decoder, the decoded picture buffercomponent 223 stores and forwards the reconstructed and filtered blockstoward a display as part of an output video signal. The decoded picturebuffer component 223 may be any memory device capable of storingprediction blocks, residual blocks, and/or reconstructed image blocks.

The header formatting and CABAC component 231 receives the data from thevarious components of codec system 200 and encodes such data into acoded bitstream for transmission toward a decoder. Specifically, theheader formatting and CABAC component 231 generates various headers toencode control data, such as general control data and filter controldata. Further, prediction data, including intra-prediction and motiondata, as well as residual data in the form of quantized transformcoefficient data are all encoded in the bitstream. The final bitstreamincludes all information desired by the decoder to reconstruct theoriginal partitioned video signal 201. Such information may also includeintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks,indications of most probable intra-prediction modes, an indication ofpartition information, etc. Such data may be encoded by employingentropy coding. For example, the information may be encoded by employingcontext adaptive variable length coding (CAVLC), CABAC, syntax-basedcontext-adaptive binary arithmetic coding (SBAC), probability intervalpartitioning entropy (PIPE) coding, or another entropy coding technique.Following the entropy coding, the coded bitstream may be transmitted toanother device (e.g., a video decoder) or archived for latertransmission or retrieval.

FIG. 3 is a block diagram illustrating an example video encoder 300.Video encoder 300 may be employed to implement the encoding functions ofcodec system 200 and/or implement steps 101, 103, 105, 107, and/or 109of operating method 100. Encoder 300 partitions an input video signal,resulting in a partitioned video signal 301, which is substantiallysimilar to the partitioned video signal 201. The partitioned videosignal 301 is then compressed and encoded into a bitstream by componentsof encoder 300.

Specifically, the partitioned video signal 301 is forwarded to anintra-picture prediction component 317 for intra-prediction. Theintra-picture prediction component 317 may be substantially similar tointra-picture estimation component 215 and intra-picture predictioncomponent 217. The partitioned video signal 301 is also forwarded to amotion compensation component 321 for inter-prediction based onreference blocks in a decoded picture buffer component 323. The motioncompensation component 321 may be substantially similar to motionestimation component 221 and motion compensation component 219. Theprediction blocks and residual blocks from the intra-picture predictioncomponent 317 and the motion compensation component 321 are forwarded toa transform and quantization component 313 for transform andquantization of the residual blocks. The transform and quantizationcomponent 313 may be substantially similar to the transform scaling andquantization component 213. The transformed and quantized residualblocks and the corresponding prediction blocks (along with associatedcontrol data) are forwarded to an entropy coding component 331 forcoding into a bitstream. The entropy coding component 331 may besubstantially similar to the header formatting and CABAC component 231.

The transformed and quantized residual blocks and/or the correspondingprediction blocks are also forwarded from the transform and quantizationcomponent 313 to an inverse transform and quantization component 329 forreconstruction into reference blocks for use by the motion compensationcomponent 321. The inverse transform and quantization component 329 maybe substantially similar to the scaling and inverse transform component229. In-loop filters in an in-loop filters component 325 are alsoapplied to the residual blocks and/or reconstructed reference blocks,depending on the example. The in-loop filters component 325 may besubstantially similar to the filter control analysis component 227 andthe in-loop filters component 225. The in-loop filters component 325 mayinclude multiple filters as discussed with respect to in-loop filterscomponent 225. The filtered blocks are then stored in a decoded picturebuffer component 323 for use as reference blocks by the motioncompensation component 321. The decoded picture buffer component 323 maybe substantially similar to the decoded picture buffer component 223.

FIG. 4 is a block diagram illustrating an example video decoder 400.Video decoder 400 may be employed to implement the decoding functions ofcodec system 200 and/or implement steps 111, 113, 115, and/or 117 ofoperating method 100. Decoder 400 receives a bitstream, for example froman encoder 300, and generates a reconstructed output video signal basedon the bitstream for display to an end user.

The bitstream is received by an entropy decoding component 433. Theentropy decoding component 433 is configured to implement an entropydecoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or otherentropy coding techniques. For example, the entropy decoding component433 may employ header information to provide a context to interpretadditional data encoded as codewords in the bitstream. The decodedinformation includes any desired information to decode the video signal,such as general control data, filter control data, partitioninformation, motion data, prediction data, and quantized transformcoefficients from residual blocks. The quantized transform coefficientsare forwarded to an inverse transform and quantization component 429 forreconstruction into residual blocks. The inverse transform andquantization component 429 may be similar to inverse transform andquantization component 329.

The reconstructed residual blocks and/or prediction blocks are forwardedto intra-picture prediction component 417 for reconstruction into imageblocks based on intra-prediction operations. The intra-pictureprediction component 417 may be similar to intra-picture estimationcomponent 215 and an intra-picture prediction component 217.Specifically, the intra-picture prediction component 417 employsprediction modes to locate a reference block in the frame and applies aresidual block to the result to reconstruct intra-predicted imageblocks. The reconstructed intra-predicted image blocks and/or theresidual blocks and corresponding inter-prediction data are forwarded toa decoded picture buffer component 423 via an in-loop filters component425, which may be substantially similar to decoded picture buffercomponent 223 and in-loop filters component 225, respectively. Thein-loop filters component 425 filters the reconstructed image blocks,residual blocks and/or prediction blocks, and such information is storedin the decoded picture buffer component 423. Reconstructed image blocksfrom decoded picture buffer component 423 are forwarded to a motioncompensation component 421 for inter-prediction. The motion compensationcomponent 421 may be substantially similar to motion estimationcomponent 221 and/or motion compensation component 219. Specifically,the motion compensation component 421 employs motion vectors from areference block to generate a prediction block and applies a residualblock to the result to reconstruct an image block. The resultingreconstructed blocks may also be forwarded via the in-loop filterscomponent 425 to the decoded picture buffer component 423. The decodedpicture buffer component 423 continues to store additional reconstructedimage blocks, which can be reconstructed into frames via the partitioninformation. Such frames may also be placed in a sequence. The sequenceis output toward a display as a reconstructed output video signal.

FIG. 5 is a schematic diagram illustrating an example bitstream 500 andsub-bitstream 501 extracted from the bitstream 500. For example, thebitstream 500 can be generated by a codec system 200 and/or an encoder300 for decoding by a codec system 200 and/or a decoder 400. As anotherexample, the bitstream 500 may be generated by an encoder at step 109 ofmethod 100 for use by a decoder at step 111.

The bitstream 500 includes a sequence parameter set (SPS) 510, aplurality of picture parameter sets (PPS s) 512, a plurality of sliceheaders 514, image data 520, and one or more SEI messages 515. An SPS510 contains sequence data common to all the pictures in the videosequence contained in the bitstream 500. Such data can include picturesizing, bit depth, coding tool parameters, bit rate restrictions, etc.The PPS 512 contains parameters that are specific to one or morecorresponding pictures. Hence, each picture in a video sequence mayrefer to one PPS 512. The PPS 512 can indicate coding tools availablefor tiles in corresponding pictures, quantization parameters, offsets,picture specific coding tool parameters (e.g., filter controls), etc.The slice header 514 contains parameters that are specific to one ormore corresponding slices 524 in a picture. Hence, each slice 524 in thevideo sequence may refer to a slice header 514. The slice header 514 maycontain slice type information, picture order counts (POCs), referencepicture lists, prediction weights, tile entry points, deblockingparameters, etc. In some examples, slices 524 may be referred to as tilegroups. In such a case, the slice header 514 may be referred to as atile group header. SEI messages 515 are optional messages that containmetadata that is not required for block decoding, but can be employedfor related purposes such as indicating picture output timing, displaysettings, loss detection, loss concealment, etc.

The image data 520 contains video data encoded according tointer-prediction and/or intra-prediction as well as correspondingtransformed and quantized residual data. Such image data 520 is sortedaccording to a partitioning used to partition the image prior toencoding. For example, the video sequence is divided into pictures 521.The pictures 521 may be further divided into sub-pictures 522, which aredivided into slices 524. The slices 524 may be further divided intotiles and/or CTUs. The CTUs are further divided into coding blocks basedon coding trees. The coding blocks can then be encoded/decoded accordingto prediction mechanisms. For example, a picture 521 can contain one ormore sub-pictures 522. A sub-picture 522 may contain one or more slices524. The picture 521 refers to the PPS 512 and the slices 524 refer tothe slice header 514. The sub-pictures 522 may be partitionedconsistently over an entire video sequence (also known as a segment),and hence may refer to the SPS 510. Each slice 524 may contain one ormore tiles. Each slice 524, and hence picture 521 and sub-picture 522,can also contain a plurality of CTUs.

Each picture 521 may contain an entire set of visual data associatedwith a video sequence for a corresponding instant in time. However,certain applications may wish to display only a portion of a picture 521in some cases. For example, a virtual reality (VR) system may display auser selected region of the picture 521, which creates the sensation ofbeing present in the scene depicted in the picture 521. The region auser may wish to view is not known when the bitstream 500 is encoded.Accordingly, the picture 521 may contain each possible region a user maypotentially view as sub-pictures 522, which can be decoded and displayedseparately based on user input. Other applications may separatelydisplay a region of interest. For example, a television with a picturein a picture may wish to display a particular region, and hence asub-picture 522, from one video sequence over a picture 521 of anunrelated video sequence. In yet another example, teleconferencingsystems may display an entire picture 521 of a user that is currentlyspeaking and a sub-picture 522 of a user that is not currently speaking.Accordingly, a sub-picture 522 may contain a defined region of thepicture 521. A sub-picture 522 that is temporarily motion constrainedcan be separately decodable from the rest of the picture 521.Specifically, a temporal motion constrained sub-picture is encodedwithout reference to samples outside of the temporal motion constrainedsub-picture, and hence contains sufficient information for completedecoding without reference to the remainder of the picture 521.

Each slice 524 may be a rectangle defined by a CTU at an upper leftcorner and a CTU at a bottom right corner. In some examples, a slice 524includes a series of tiles and/or CTUs in a raster scan order proceedingfrom left to right and top to bottom. In other examples, a slice 524 isa rectangular slice. A rectangular slice may not traverse the entirewidth of a picture according to a raster scan order. Instead, arectangular slice may contain a rectangular and/or square region of apicture 521 and/or sub-picture 522 defined in terms of a CTU and/or tilerows and a CTU and/or tile columns. A slice 524 is the smallest unitthat can be separately displayed by a decoder. Hence, slices 524 from apicture 521 may be assigned to different sub-pictures 522 to separatelydepict desired regions of a picture 521.

A decoder may display one or more sub-pictures 523 of the picture 521.Sub-pictures 523 are a user selected or a pre-defined sub-group ofsub-pictures 522. For example, a picture 521 may be divided into ninesub-pictures 522, but the decoder may only display a single sub-picture523 from the group of sub-pictures 522. The sub-pictures 523 containslices 525, which are a selected or predefined sub-group of slices 524.To allow for separate display of the sub-pictures 523, a sub-bitstream501 may be extracted 529 from the bitstream 500. The extraction 529 mayoccur on the encoder side so that the decoder only receives thesub-bitstream 501. In other cases, the entire bitstream 500 istransmitted to the decoder and the decoder extracts 529 thesub-bitstream 501 for separate decoding. It should be noted that thesub-bitstream 501 may also be referred to generally as a bitstream insome cases. A sub-bitstream 501 includes the SPS 510, the PPS 512, theselected sub-pictures 523, as well as slice headers 514, and SEImessages 515 that are relevant to the sub-pictures 523 and/or slices525.

The present disclosure signals various data to support efficient codingof the sub-pictures 522 for selection and display of the sub-pictures523 at the decoder. The SPS 510 includes a sub-picture size 531, asub-picture location 532, and sub-picture IDs 533 related to thecomplete set of sub-pictures 522. The sub-picture size 531 includes asub-picture height in luma samples and a sub-picture width in lumasamples for a corresponding sub-picture 522. The sub-picture location532 includes an offset distance between a top-left sample of acorresponding sub-picture 522 and a top-left sample of the picture 521.The sub-picture location 532 and the sub-picture size 531 define alayout of the corresponding sub-picture 522. The sub-picture ID 533contains data that uniquely identifies a corresponding sub-picture 522.The sub-picture ID 533 may be a sub-picture 522 raster scan index orother defined value. Hence, a decoder can read the SPS 510 and determinethe size, location, and ID of each sub-picture 522. In some video codingsystems, data related to sub-pictures 522 may be included in the PPS 512because a sub-picture 522 is partitioned from a picture 521. However,partitions used to create sub-pictures 522 may be used by applications,such as ROI based applications, VR applications, etc., that depend onconsistent sub-picture 522 partitions over a video sequence/segment. Assuch, sub-picture 522 partitions generally do not change on a perpicture basis. Placing layout information for sub-pictures 522 in theSPS 510 ensures that the layout is only signaled once for asequence/segment rather than redundantly signaled for each PPS 512(which may be signaled for each picture 521 in some cases). Also,signaling the sub-picture 522 information, instead of relying on thedecoder to derive such information, reduces the possibility of error incase of lost packets and supports additional functionality in terms ofextracting sub-pictures 523. Accordingly, signaling sub-picture 522layout in the SPS 510 improves the functionality of an encoder and/ordecoder.

The SPS 510 also contains motion constrained sub-pictures flags 534related to the complete set of sub-pictures 522. The motion constrainedsub-pictures flags 534 indicate whether each sub-picture 522 is atemporal motion constrained sub-picture. Hence, the decoder can read themotion constrained sub-pictures flags 534 and determine which of thesub-pictures 522 can be separately extracted and displayed withoutdecoding other sub-pictures 522. This allows selected sub-pictures 522to be coded as temporal motion constrained sub-pictures while allowingother sub-pictures 522 to be coded without such restrictions forincreased coding efficiency.

The sub-picture IDs 533 are also included in the slice headers 514. Eachslice header 514 contains data relevant to a corresponding set of slices524. Accordingly, the slice header 514 contains only the sub-picture IDs533 corresponding to the slices 524 associated with the slice header514. As such, a decoder can receive a slice 524, obtain a sub-picture ID533 from the slice header 514, and determine which sub-picture 522contains the slice 524. The decoder can also use the sub-picture ID 533from the slice header 514 to correlate with related data in the SPS 510.As such, the decoder can determine how to position the sub-pictures522/523 and slices 524/525 by reading the SPS 510 and relevant sliceheaders 514. This allows the sub-pictures 523 and slices 525 to bedecoded even if some sub-pictures 522 are lost in transmission orpurposely omitted to increase coding efficiency.

The SEI message 515 may also contain a sub-picture level 535. Thesub-picture level 535 indicates hardware resources needed to decode acorresponding sub-picture 522. In this way, each sub-picture 522 can becoded independently of other sub-pictures 522. This ensures eachsub-picture 522 can be allocated the correct amount of hardwareresources at the decoder. Without such a sub-picture level 535, eachsub-picture 522 would be allocated with enough resources to decode themost complex sub-picture 522. Hence, the sub-picture level 535 preventsthe decoder from over allocating hardware resources if sub-pictures 522are associated with varying hardware resource requirements.

FIG. 6 is a schematic diagram illustrating an example picture 600partitioned into sub-pictures 622. For example, a picture 600 can beencoded in and decoded from a bitstream 500, for example by a codecsystem 200, an encoder 300, and/or a decoder 400. Further, the picture600 can be partitioned and/or included in a sub-bitstream 501 to supportencoding and decoding according to method 100.

The picture 600 may be substantially similar to a picture 521. Further,the picture 600 may be partitioned into sub-pictures 622, which aresubstantially similar to sub-pictures 522. The sub-pictures 622 eachinclude a sub-picture size 631, which may be included in a bitstream 500as a sub-picture size 531. The sub-picture size 631 includes sub-picturewidth 631 a and a sub-picture height 631 b. The sub-picture width 631 ais the width of a corresponding sub-picture 622 in units of lumasamples. The sub-picture height 631 b is the height of a correspondingsub-picture 622 in units of luma samples. The sub-pictures 622 eachinclude a sub-picture ID 633, which may be included in a bitstream 500as a sub-picture ID 633. The sub-picture ID 633 may be any value thatuniquely identifies each sub-picture 622. In the example shown, thesub-picture ID 633 is a sub-picture 622 index. The sub-pictures 622 eachinclude a location 632, which may be included in a bitstream 500 as asub-picture location 532. The location 632 is expressed as an offsetbetween the top left sample of a corresponding sub-picture 622 and a topleft sample 642 of the picture 600.

Also as shown, some sub-pictures 622 may be temporal motion constrainedsub-pictures 634 and other sub-pictures 622 may not. In the exampleshown, the sub-picture 622 with a sub-picture ID 633 of five is atemporal motion constrained sub-picture 634. This indicates that thesub-picture 622 identified as five is coded without reference to anyother sub-picture 622 and can therefore be extracted and separatelydecoded without considering data from the other sub-pictures 622. Anindication of which sub-pictures 622 are temporal motion constrainedsub-pictures 634 can be signaled in a bitstream 500 in motionconstrained sub-pictures flags 534.

As shown, the sub-pictures 622 can be constrained to cover a picture 600without a gap or an overlap. A gap is a region of a picture 600 that isnot included in any sub-picture 622. An overlap is a region of a picture600 that is included in more than one sub-picture 622. In the exampleshown in FIG. 6 , the sub-pictures 622 are partitioned from the picture600 to prevent both gaps and overlaps. Gaps cause picture 600 samples tobe left out of the sub-pictures 622. Overlaps cause associated slices tobe included in multiple sub-pictures 622. Therefore, gaps and overlapsmay cause samples to be impacted by differential treatment whensub-pictures 622 are coded differently. If this is allowed at theencoder, a decoder must support such a coding scheme even when thedecoding scheme is rarely used. By disallowing sub-picture 622 gaps andoverlaps, the complexity of the decoder can be decreased as the decoderis not required to account for potential gaps and overlaps whendetermining sub-picture sizes 631 and locations 632. Further,disallowing sub-picture 622 gaps and overlaps reduces complexity of RDOprocesses at the encoder. This is because the encoder can omitconsidering gap and overlap cases when selecting an encoding for a videosequence. Accordingly, avoiding gaps and overlaps may reduce the usageof memory resources and/or processing resources at the encoder and thedecoder.

FIG. 7 is a schematic diagram illustrating an example mechanism 700 forrelating slices 724 to a sub-picture 722 layout. For example, themechanism 700 may applied to picture 600. Further, mechanism 700 can beapplied based on data in a bitstream 500, for example by a codec system200, an encoder 300, and/or a decoder 400. Further, the mechanism 700can be employed to support encoding and decoding according to method100.

The mechanism 700 can be applied to slices 724 in a sub-picture 722,such as slices 524/525 and sub-pictures 522/523, respectively. In theexample shown, the sub-picture 722 includes a first slice 724 a, asecond slice 724 b, and a third slice 724 c. The slice headers for eachof the slices 724 include a sub-picture ID 733 for the sub-picture 722.The decoder can match the sub-picture ID 733 from the slice header withthe sub-picture ID 733 in the SPS. The decoder can then determine thelocation 732 and size of the sub-picture 722 from the SPS based on thesub-picture ID 733. Using the location 732, the sub-picture 722 can beplaced relative to the top left sample in the top left corner 742 of thepicture. The size can be used to set the height and the width of thesub-picture 722 relative to the location 732. The slices 724 can then beincluded in the sub-picture 722. Accordingly, the slices 724 can bepositioned in the correct sub-picture 722 based on the sub-picture ID733 without reference to other sub-pictures. This supports errorcorrection as other lost sub-pictures do not alter the decoding ofsub-picture 722. This also supports applications that only extract asub-picture 722 and avoid transmitting other sub-pictures. Hence, thesub-picture IDs 733 support increased functionality and/or increasedcoding efficiency, which reduces the usage of network resources, memoryresources, and/or processing resources at the encoder and the decoder.

FIG. 8 is a schematic diagram illustrating another example picture 800partitioned into sub-pictures 822. Picture 800 may be substantiallysimilar to picture 600. In addition, a picture 800 can be encoded in anddecoded from a bitstream 500, for example by a codec system 200, anencoder 300, and/or a decoder 400. Further, the picture 800 can bepartitioned and/or included in a sub-bitstream 501 to support encodingand decoding according to method 100 and/or mechanism 700.

Picture 800 includes sub-pictures 822, which may be substantiallysimilar to sub-pictures 522, 523, 622, and/or 722. The sub-pictures 822are divided into a plurality of CTUs 825. A CTU 825 is a basic codingunit in standardized video coding systems. A CTU 825 is sub-divided by acoding tree into coding blocks, which are coded according tointer-prediction or intra-prediction. As shown, some sub-pictures 822 aare constrained to include sub-picture widths and sub-picture heightsthat are multiples of CTU 825 size. In the example shown, sub-pictures822 a have a height of six CTUs 825 and a width of five CTUs 825. Thisconstraint is removed for sub-pictures 822 b positioned on the picturesright border 801 and for sub-pictures 822 c positioned on the picturesbottom border 802. In the example shown, sub-pictures 822 b have a widthof between five and six CTUs 825. Hence, sub-pictures 822 b have a widthof five complete CTUs 825 and one incomplete CTU 825. However,sub-pictures 822 b that are not positioned on the pictures bottom border802 are still constrained to maintain a sub-picture height that is amultiple of CTU 825 size. In the example shown, sub-pictures 822 c havea height of between six and seven CTUs 825. Hence, sub-pictures 822 chave a height of six complete CTUs 825 and one incomplete CTU 825.However, sub-pictures 822 c that are not positioned on the picturesright border 801 are still constrained to maintain a sub-picture widththat is a multiple of CTU 825 size. It should be noted that the picturesright border 801 and the pictures bottom border 802 may also be referredto as the pictures right boundary and the pictures bottom boundary,respectively. It should also be noted that the CTU 825 size is a userdefined value. The CTU 825 size may be any value between a minimum CTU825 size and a maximum CTU 825 size. For example, the minimum CTU 825size may be sixteen luma samples in height and sixteen luma samples inwidth. Further, the maximum CTU 825 size may be one hundred twenty eightluma samples in height and one hundred twenty eight luma samples inwidth.

As noted above, some video systems may limit sub-pictures 822 to includeheights and widths that are multiples of CTU 825 size. This may preventsub-pictures 822 from operating correctly with many picture layouts, forexample with a picture 800 that contains a total width or height that isnot a multiple of CTU 825 size. By allowing the bottom sub-pictures 822c and right sub-pictures 822 b to include heights and widths,respectively, that are not multiples of CTU 825 size, sub-pictures 822may be used with any picture 800 without causing decoding errors. Thisresults in increasing encoder and decoder functionality. Further, theincreased functionality allows an encoder to code pictures moreefficiently, which reduces the usage of network resources, memoryresources, and/or processing resources at the encoder and the decoder.

As described herein, the present disclosure describes designs forsub-picture based picture partitioning in video coding. A sub-picture isa rectangular area within a picture that can be decoded independentlyusing a similar decoding process as is used for a picture. The presentdisclosure relates to the signaling of sub-pictures in a coded videosequence and/or bitstream as well as the process for sub-pictureextraction. The descriptions of the techniques are based on VVC by theJVET of ITU-T and ISO/IEC. However, the techniques also apply to othervideo codec specifications. The following are example embodimentsdescribed herein. Such embodiments can be applied individually or incombination.

Information related to sub-pictures that may be present in the codedvideo sequence (CVS) may be signaled in a sequence level parameter set,such as an SPS. Such signaling may include the following information.The number of sub-pictures that are present in each picture of the CVSmay be signaled in the SPS. In the context of the SPS or a CVS, thecollocated sub-pictures for all the access units (AUs) may collectivelybe referred to as a sub-picture sequence. A loop for further specifyinginformation describing properties of each sub-picture may also beincluded in the SPS. This information may comprise the sub-pictureidentification, the location of the sub-picture (e.g., the offsetdistance between the top-left corner luma sample of the sub-picture andthe top-left corner luma sample of the picture), and the size of thesub-picture. In addition, the SPS may signal whether each sub-picture isa motion-constrained sub-picture (containing the functionality of anMCTS). Profile, tier, and level information for each sub-picture mayalso be signaled or be derivable at the decoder. Such information may beemployed to determine profile, tier, and level information for abitstream created by extracting sub-pictures from the originalbitstream. The profile and tier of each sub-picture may be derived to bethe same as the entire bitstream's profile and tier. The level for eachsub-picture may be signaled explicitly. Such signaling may be present inthe loop contained in the SPS. The sequence-level hypothetical referencedecoder (HRD) parameters may be signaled in the video usabilityinformation (VUI) section of the SPS for each sub-picture (orequivalently, each sub-picture sequence).

When a picture is not partitioned into two or more sub-pictures, theproperties of the sub-picture (e.g., location, size, etc.), except thesub-picture ID, may be not present/signaled in the bitstream. When asub-picture of pictures in a CVS is extracted, each access unit in thenew bitstream may contain no sub-pictures. In this case, the picture ineach AU in the new bitstream is not partitioned into multiplesub-pictures. Thus there is no need to signal sub-picture propertiessuch as location and size in the SPS since such information can bederived from the picture properties. However, the sub-pictureidentification may still be signaled as the ID may be referred to by VCLNAL units/tile groups that are included in the extracted sub-picture.This may allow the sub-picture IDs to remain the same when extractingthe sub-picture.

The location of a sub-picture in the picture (x offset and y offset) canbe signaled in units of luma samples. The location represents thedistance between the top-left corner luma sample of the sub-picture andtop-left corner luma sample of the picture. Alternatively, the locationof a sub-picture in the picture can be signaled in units of the minimumcoding luma block size (MinCbSizeY). Alternatively, the unit ofsub-picture location offsets may be explicitly indicated by a syntaxelement in a parameter set. The unit may be CtbSizeY, MinCbSizeY, lumasample, or other values.

The size of a sub-picture (sub-picture width and sub-picture height) canbe signaled in units of luma samples. Alternatively, the size of asub-picture can be signaled in units of the minimum coding luma blocksize (MinCbSizeY). Alternatively, the unit of sub-picture size valuescan be explicitly indicated by a syntax element in a parameter set. Theunit may be CtbSizeY, MinCbSizeY, luma sample, or other values. When asub-picture's right border does not coincide with picture's rightborder, the sub-picture's width may be required to be an integermultiple of luma CTU size (CtbSizeY). Likewise, when a sub-picture'sbottom border does not coincide with picture's bottom border, thesub-picture's height may be required to be an integer multiple of lumaCTU size (CtbSizeY). If a sub-picture's width is not an integer multipleof luma CTU size, the sub-picture may be required to be located at aright most position in the picture. Likewise, if a sub-picture's heightis not an integer multiple of luma CTU size, the sub-picture may berequired to be located at a bottom most position in the picture. In somecases, a sub-picture's width can be signaled in units of luma CTU size,but the width of a sub-picture is not an integer multiple of luma CTUsize. In this case, the actual width in luma samples can be derivedbased on the sub-picture's offset location. The sub-picture's width canbe derived based on luma CTU size and the picture's height can bederived based on luma samples. Likewise, a sub-picture's height may besignaled in units of luma CTU size, but the height of the sub-picture isnot an integer multiple of luma CTU size. In such a case, the actualheight in luma sample can be derived based on the sub-picture's offsetlocation. The sub-picture's height can be derived based on luma CTU sizeand the picture's height can be derived based on luma samples.

For any sub-picture, the sub-picture ID may be different from thesub-picture index. The sub-picture index may be the index of thesub-picture as signaled in a loop of sub-pictures in the SPS. Thesub-picture ID may be the index of the sub-picture in sub-picture rasterscan order in the picture. When the value of the sub-picture ID of eachsub-picture is the same as the sub-picture index, the sub-picture ID maybe signaled or derived. When the sub-picture ID of each sub-picture isdifferent from the sub-picture index, the sub-picture ID is explicitlysignaled. The number of bits for signaling of sub-picture IDs may besignaled in the same parameter set that contains sub-picture properties(e.g., in the SPS). Some values for sub-picture ID may be reserved forcertain purposes. For example, when tile group headers containsub-picture IDs to specify which sub-picture contains a tile group, thevalue zero may be reserved and not used for sub-pictures to ensure thatthe first few bits of a tile group header are not all zeros to avoidaccidental inclusion of an emulation prevention code. In optional caseswhere sub-pictures of a picture do not cover the whole area of thepicture without gap and without overlap, a value (e.g., value one) maybe reserved for tile groups that are not part of any sub-picture.Alternatively, the sub-picture ID of the remaining area is explicitlysignaled. The number of bits for signaling sub-picture ID may beconstrained as follows. The value range should be enough to uniquelyidentify all sub-pictures in a picture, including the reserved values ofsub-picture ID. For example, the minimum number of bits for sub-pictureID can be the value of Ceil(Log 2(number of sub-pictures in apicture+number of reserved sub-picture ID).

It may be constrained that the union of sub-pictures must cover thewhole picture without gap and without overlap. When this constraint isapplied, for each sub-picture, a flag may be present to specify whetherthe sub-picture is a motion-constrained sub-picture, which indicates thesub-picture can be extracted. Alternatively, the union of sub-picturesmay not cover the whole picture, but overlaps may not be allowed.

Sub-picture IDs may be present immediately after the NAL unit header toassist the sub-picture extraction process without requiring theextractor to parse the remainder of the NAL unit bits. For VCL NALunits, the sub-picture ID may be present in the first bits of tile groupheaders. For non-VCL NAL unit, the following may apply. For SPS, thesub-picture ID need not be present immediately after the NAL unitheader. For PPS, if all tile groups of the same picture are constrainedto refer to the same PPS, the sub-picture ID need not be presentimmediately after its NAL unit header. If tile groups of the samepicture are allowed to refer to different PPSs, the sub-picture ID maybe present in the first bits of PPS (e.g., immediately after the NALunit header). In this case, any tile groups of one picture may beallowed to share the same PPS. Alternatively, when tile groups of thesame picture are allowed to refer to different PPSs, and different tilegroup of the same picture are also allowed to share the same PPS, nosub-picture ID may be present in the PPS syntax. Alternatively, whentile groups of the same picture are allowed to refer to different PPSs,and different tile group of the same picture are also allowed to sharethe same PPS, a list of sub-picture IDs may be present in the PPSsyntax. The list indicates the sub-pictures to which the PPS applies.For other non-VCL NAL units, if the non-VCL unit applies to the picturelevel or above (e.g., access unit delimiter, end of sequence, end ofbitstream, etc.), then the sub-picture ID may not be present immediatelyafter the NAL unit header. Otherwise, the sub-picture ID may be presentimmediately after the NAL unit header.

With the above SPS signaling, the tile partitioning within individualsub-pictures may be signaled in the PPS. Tile groups within the samepicture may be allowed to refer to different PPSs. In this case, tilegrouping may only be within each sub-picture. The tile grouping conceptis partitioning of a sub-picture into tiles.

Alternatively, a parameter set for describing the tile partitioningwithin individual sub-pictures is defined. Such a parameter set may becalled Sub-Picture Parameter Set (SPPS). The SPPS refers to SPS. Asyntax element referring to the SPS ID is present in SPPS. The SPPS maycontain a sub-picture ID. For sub-picture extraction purposes, thesyntax element referring to the sub-picture ID is the first syntaxelement in SPPS. The SPPS contains a tile structure (e.g., a number ofcolumns, a number of rows, uniform tile spacing, etc.) The SPPS maycontain a flag to indicate whether or not a loop filter is enabledacross associated sub-picture boundaries. Alternatively, the sub-pictureproperties for each sub-picture may be signaled in the SPPS instead ofin the SPS. Tile partitioning within individual sub-pictures may stillbe signaled in the PPS. Tile groups within the same picture are allowedto refer to different PPSs. Once an SPPS is activated, the SPPS lastsfor a sequence of consecutive AUs in decoding order. However, the SPPSmay be deactivated/activated at an AU that is not the start of a CVS. Atany moment during the decoding process of a single-layer bitstream withmultiple sub-pictures at some AUs, multiple SPPSs may be active. An SPPSmay be shared by different sub-pictures of an AU. Alternatively, SPPSand PPS can be merged into one parameter set. In such a case, all tilegroups of the same picture may not be required to refer to the same PPS.A constraint may be applied such that all tile groups in the samesub-picture may refer to the same parameter set resulting from themerger between SPPS and PPS.

The number of bits used for signaling sub-picture ID may be signaled ina NAL unit header. When present in a NAL unit header such informationmay assist sub-picture extraction processes in parsing sub-picture IDvalue at the beginning of a NAL unit's payload (e.g., the first few bitsimmediately after NAL unit header). For such signaling, some of thereserved bits (e.g., seven reserved bits) in a NAL unit header may beused to avoid increasing the length of NAL unit header. The number ofbits for such signaling may cover the value of sub-picture-ID-bit-len.For example, four bits out of seven reserved bits of a VVCs NAL unitheader may be used for this purpose.

When decoding a sub-picture, the location of each coding tree block(e.g., xCtb and yCtb) may be adjusted to an actual luma sample locationin the picture instead of a luma sample location in the sub-picture. Inthis way, extraction of a co-located sub-picture from each referencepicture can be avoided as the coding tree block is decoded withreference to the picture instead of the sub-picture. For adjusting thelocation of a coding tree block, the variables SubpictureXOffset andSubpictureYOffset can be derived based on the sub-picture position(subpic_x_offset and subpic_y_offset). The values of the variables maybe added to the values of the luma sample location x and y coordinates,respectively, of each coding tree block in the sub-picture.

A sub-picture extraction process can be defined as follows. The input tothe process is the target sub-picture to be extracted. This can be inthe form of sub-picture ID or sub-picture location. When the input is asub-picture's location, the associated sub-picture ID can be resolved byparsing the sub-picture information in the SPS. For non-VCL NAL units,the following apply. Syntax elements in the SPS related to picture sizeand level may be updated with the sub-picture's size and levelinformation. The following non-VCL NAL units are kept without change:PPS, Access Unit Delimiter (AUD), End of Sequence (EOS), End ofBitstream (EOB), and any other non-VCL NAL units that are applicable topicture level or above. The remaining non-VCL NAL units with sub-pictureID not equal to the target sub-picture ID may be removed. VCL NAL unitswith sub-picture ID not equal to the target sub-picture ID may also beremoved.

A sequence level sub-picture nesting SEI message may be used for nestingof AU-level or sub-picture level SEI messages for a set of sub-pictures.This may include a buffering period, picture timing, and non-HRD SEImessages. The syntax and semantics of this sub-picture nesting SEImessage can be as follows. For systems operations, such as inomnidirectional media format (OMAF) environments, a set of sub-picturesequences covering a viewport may be requested and decoded by the OMAFplayer. Therefore, the sequence level SEI message is used to carryinformation of a set of sub-picture sequences that collectively cover ofa rectangular picture region. The information can be used by systems,and the information is indicative of the required decoding capability aswell as the bitrate of the set of sub-picture sequences. The informationindicates the level of the bitstream including only the set ofsub-picture sequences. This information also indicates the bit rate ofthe bitstream containing only the set of sub-picture sequences.Optionally, a sub-bitstream extraction process may be specified for aset of sub-picture sequences. The benefit of doing this is the bitstreamincluding only a set of sub-picture sequences can also be conforming. Adisadvantage is that in considering different viewport sizepossibilities there can be many such sets in addition to the alreadylarge possible numbers of individual sub-picture sequences.

In an example embodiment, one or more of the disclosed examples may beimplemented as follows. A sub-picture may be defined as a rectangularregion of one or more tile groups within a picture. An allowed binarysplit process may be defined as follows. The inputs to this process are:a binary split mode btSplit, a coding block width cbWidth, a codingblock height cbHeight, a location (x0, y0) of the top-left luma sampleof the considered coding block relative to the top-left luma sample ofthe picture, a multi-type tree depth mttDepth, a maximum multi-type treedepth with offset maxMttDepth, a maximum binary tree size maxBtSize, anda partition index partIdx. The output of this process is the variableallowBtSplit.

btSplit = = SPLIT_BT_VER btSplit = = SPLIT_BT_HOR parallelTtSplitSPLIT_TT_VER SPLIT_TT_HOR cbSize cbWidth cbHeight

Specification of parallelTtSplit and cbSize Based on btSplit

The variables parallelTtSplit and cbSize are derived as specified above.The variable allowBtSplit is derived as follows. If one or more of thefollowing conditions are true, allowBtSplit is set equal to FALSE:cbSize is less than or equal to MinBtSizeY, cbWidth is greater thanmaxBtSize, cbHeight is greater than maxBtSize, and mttDepth is greaterthan or equal to maxMttDepth. Otherwise, if all of the followingconditions are true, allowBtSplit is set equal to FALSE: btSplit isequal to SPLIT_BT_VER, and y0+cbHeight is greater thanSubPicBottomBorderInPic. Otherwise, if all of the following conditionsare true, allowBtSplit is set equal to FALSE, btSplit is equal toSPLIT_BT_HOR, x0+cbWidth is greater than SubPicRightBorderinPic, andy0+cbHeight is less than or equal to SubPicBottomBorderInPic. Otherwise,if all of the following conditions are true, allowBtSplit is set equalto FALSE: mttDepth is greater than zero, partIdx is equal to one, andMttSplitMode[x0][y0][mttDepth−1] is equal to parallelTtSplit. Otherwiseif all of the following conditions are true, allowBtSplit is set equalto FALSE: btSplit is equal to SPLIT_BT_VER, cbWidth is less than orequal to MaxTbSizeY, and cbHeight is greater than MaxTbSizeY. Otherwiseif all of the following conditions are true, allowBtSplit is set equalto FALSE: btSplit is equal to SPLIT_BT_HOR, cbWidth is greater thanMaxTbSizeY, and cbHeight is less than or equal to MaxTbSizeY. Otherwise,allowBtSplit is set equal to TRUE.

An allowed ternary split process may be defined as follows. Inputs tothis process are: a ternary split mode ttSplit, a coding block widthcbWidth, a coding block height cbHeight, a location (x0, y0) of thetop-left luma sample of the considered coding block relative to thetop-left luma sample of the picture, a multi-type tree depth mttDepth, amaximum multi-type tree depth with offset maxMttDepth, and a maximumbinary tree size maxTtSize. The output of this process is the variableallowTtSplit.

ttSplit = = SPLIT_TT_VER ttSplit = = SPLIT_TT_HOR cbSize cbWidthcbHeight

Specification of cbSize Based on ttSplit

The variable cbSize is derived as specified above. The variableallowTtSplit is derived as follows. If one or more of the followingconditions are true, allowTtSplit is set equal to FALSE: cbSize is lessthan or equal to 2*MinTtSizeY, cbWidth is greater than Min(MaxTbSizeY,maxTtSize), cbHeight is greater than Min(MaxTbSizeY, maxTtSize),mttDepth is greater than or equal to maxMttDepth, x0+cbWidth is greaterthan SubPicRightBorderInPic, and y0+cbHeight is greater thanSubPicBottomBorderinPic. Otherwise, allowTtSplit is set equal to TRUE.

Sequence parameter set RBSP syntax and semantics are as follows.

Descriptor seq_parameter_set_rbsp( ) {   sps_seq_parameter_set_id ue(v)  pic_width_in_luma_samples ue(v)   pic_height_in_luma samples ue(v)  num_subpic_minus1 ue(v)   subpic_id_len_minus1 ue(v)   for ( i = 0; i<= num_subpic_minus1; i++ ) {    subpic_id[ i ] u(v)    if(num_subpic_minus1 > 0 ){     subpic_level_idc[ i ] u(8)    subpic_x_offset[ i ] ue(v)     subpic_y_offset[ i ] ue(v)    subpic_width_in_luma_samples[ i ] ue(v)    subpic_height_in_luma_samples[ i ] ue(v)    subpic_motion_constrained_flag[ i ] u(1)    }   } . . . }

The pic_width_in_luma_samples specifies the width of each decodedpicture in units of luma samples. pic_width_in_luma_samples shall not beequal to zero and shall be an integer multiple of MinCbSizeY. Thepic_height_in_luma_samples specifies the height of each decoded picturein units of luma samples. pic_height_in_luma_samples shall not be equalto zero and shall be an integer multiple of MinCbSizeY. Thenum_subpicture_minus1 plus 1 specifies the number of sub-picturespartitioned in coded pictures belong to the coded video sequence. Thesubpic_id_len_minus1 plus 1 specifies the number of bits used torepresent the syntax element subpic_id[i] in SPS, spps_subpic_id in SPPSreferring to the SPS, and tile_group_subpic_id in tile group headersreferring to the SPS. The value of subpic_id_len_minus1 shall be in therange of Ceil(Log 2(num_subpic_minus1+2) to eight, inclusive. Thesubpic_id[i] specifies the sub-picture ID of the i-th sub-picture ofpictures referring to the SPS. The length of subpic_id[i] issubpic_id_len_minus1+1 bits. The value of subpic_id[i] shall be greaterthan zero. The subpic_level_idc[i] indicates a level to which the CVSresulted from extraction of the i-th sub-pictures conforms to specifiedresource requirements. Bitstreams shall not contain values ofsubpic_level_idc[i] other than those specified. Other values ofsubpic_level_idc[i] are reserved. When not present, the value ofsubpic_level_idc[i] is inferred to be equal to the value ofgeneral_level_idc.

The subpic_x_offset[i] specifies the horizontal offset of the top-leftcorner of the i-th sub-picture relative to the top-left corner of thepicture. When not present, the value of subpic_x_offset[i] is inferredto be equal to 0. The value of sub-picture x offset is derived asfollows: SubpictureXOffset[i]=subpic_x_offset[i]. The subpic_y_offset[i]specifies the vertical offset of the top-left corner of the i-thsub-picture relative to the top-left corner of the picture. When notpresent, the value of subpic_y_offset[i] is inferred to be equal tozero. The value of sub-picture y offset is derived as follows:SubpictureYOffset[i]=subpic_y_offset[i]. Thesubpic_width_in_luma_samples[i] specifies the width of the i-th decodedsub-picture for which this SPS is the active SPS. When the sum ofSubpictureXOffset[i] and subpic_width_in_luma_samples[i] is less thanpic_width_in_luma_samples, the value of subpic_width_in_luma_samples[i]shall be an integer multiple of CtbSizeY. When not present, the value ofsubpic_width_in_luma_samples[i] is inferred to be equal to the value ofpic_width_in_luma_samples. The subpic_height_in_luma_samples[i]specifies the height of the i-th decoded sub-picture for which this SPSis the active SPS. When the sum of SubpictureYOffset[i] andsubpic_height_in_luma_samples[i] is less thanpic_height_in_luma_samples, the value ofsubpic_height_in_luma_samples[i] shall be an integer multiple ofCtbSizeY. When not present, the value ofsubpic_height_in_luma_samples[i] is inferred to be equal to the value ofpic_height_in_luma_samples.

It is a requirement of bitstream conformance that the union ofsub-pictures shall cover the whole area of a picture without overlap andgap. The subpic_motion_constrained_flag[i] equal to one specifies thei-th sub-picture is a temporal-motion constrained sub-picture. Thesubpic_motion_constrained_flag[i] equal to zero specifies the i-thsub-picture may or may not be a temporal motion-constrained sub-picture.When not present, the value of subpic_motion_constrained_flag isinferred to be equal to zero.

The variables SubpicWidthInCtbsY, SubpicHeightInCtbsY,SubpicSizeInCtbsY, SubpicWidthInMinCbsY, SubpicHeightInMinCbsY,SubpicSizeInMinCbsY, SubpicSizeInSamplesY, SubpicWidthInSamplesC, andSubpicHeightInSamplesC are derived as follows:

-   -   SubpicWidthInLumaSamples[i]=subpic_width_in_luma_samples[i]    -   SubpicHeightInLumaSamples[i]=subpic_height_in_luma_samples[i]    -   SubPicRightBorderinPic[i]=SubpictureXOffset[i]+PicWidthInLumaSamples[i]    -   SubPicBottomBorderinPic[i]=SubpictureYOffset[i]+PicHeightInLumaSamples[i]    -   SubpicWidthInCtbsY[i]=Ceil(SubpicWidthInLumaSamples[i]÷        CtbSizeY)    -   SubpicHeightInCtbsY[i]=Ceil(SubpicHeightInLumaSamples[i]÷CtbSizeY)    -   SubpicSizeInCtbsY[i]=SubpicWidthInCtbsY[i]*SubpicHeightInCtbsY[i]    -   SubpicWidthInMinCbsY[i]=SubpicWidthInLumaSamples[i]/MinCbSizeY    -   SubpicHeightInMinCbsY[i]=SubpicHeightInLumaSamples[i]/MinCbSizeY    -   SubpicSizeInMinCbsY[i]=SubpicWidthInMinCbsY[i]*SubpicHeightInMinCbsY[i]    -   SubpicSizeInSamplesY[i]=SubpicWidthInLumaSamples[i]*SubpicHeightInLumaSamples[i]    -   SubpicWidthInSamplesC[i]=SubpicWidthInLumaSamples[i]/SubWidthC    -   SubpicHeightInSamplesC[i]=SubpicHeightInLumaSamples[i]/SubHeightC

The sub-picture parameter set RBSP syntax and semantics are as follows.

Descriptor sub_pic_parameter_set_rbsp( ) {   spps_subpic_id u(v)  spps_subpic_parameter_set_id ue(v)   spps_seq_parameter_set_id ue(v)  single_tile_in_subpic_flag u(1)   if( !single_tile_in_subpic_flag ) {   num_tile_columns_minus1 ue(v)    num_tile_rows_minus1 ue(v)   uniform_tile_spacing_flag u(1)    if( !uniform_tile_spacing_flag ) {    for( i = 0; i < num_tile_columns_minus1; i++ )     tile_column_width_minus1[ i ] ue(v)     for( i = 0; i <num_tile_rows_minus1; i++ )      tile_row_height_minus1[ i ] ue(v)    }   loop_filter_across_tiles_enabled_flag u(1)   }   if(loop_filter_across_tiles_enabled_flag )   loop_filter_across_subpic_enabled_flag u(1)   rbsp_trailing_bits( ) }

The spps_subpic_id identifies the sub-picture which the SPPS belongs to.The length of spps_subpic_id is subpic_id_len_minus1+1 bits. Thespps_subpic_parameter_set_id identifies the SPPS for reference by othersyntax elements. The value of spps_subpic_parameter_set_id shall be inthe range of zero to sixty three, inclusive. Thespps_seq_parameter_set_id specifies the value ofsps_seq_parameter_set_id for the active SPS. The value ofspps_seq_parameter_set_id shall be in the range of zero to fifteen,inclusive. The single_tile_in_subpic_flag equal to one specifies thatthere is only one tile in each sub-picture referring to the SPPS. Thesingle_tile_in_subpic_flag equal to zero specifies that there is morethan one tile in each sub-picture referring to the SPPS. Thenum_tile_columns_minus1 plus 1 specifies the number of tile columnspartitioning the sub-picture. The num_tile_columns_minus1 shall be inthe range of zero to PicWidthInCtbsY[spps_subpic_id]−1, inclusive. Whennot present, the value of num_tile_columns_minus1 is inferred to beequal to zero. The num_tile_rows_minus1 plus 1 specifies the number oftile rows partitioning the sub-picture. The num_tile_rows_minus1 shallbe in the range of zero to PicHeightInCtbsY[spps_subpic_id]−1,inclusive. When not present, the value of num_tile_rows_minus1 isinferred to be equal to zero.

The variable NumTileslnPic is set equal to(num_tile_columns_minus1+1)*(num_tile_rows_minus1+1).

When single_tile_in_subpic_flag is equal to zero, NumTilesInPic shall begreater than zero. The uniform_tile_spacing_flag equal to one specifiesthat tile column boundaries and likewise tile row boundaries aredistributed uniformly across the sub-picture. Theuniform_tile_spacing_flag equal to zero specifies that tile columnboundaries and likewise tile row boundaries are not distributeduniformly across the sub-picture but signaled explicitly using thesyntax elements tile_column_width_minus1 [i] and tile_row_height_minus1[i]. When not present, the value of uniform_tile_spacing_flag isinferred to be equal to one. The tile_column_width_minus1[i] plus 1specifies the width of the i-th tile column in units of CTBs. Thetile_row_height_minus1 [i] plus 1 specifies the height of the i-th tilerow in units of CTBs.

The following variables are derived by invoking the CTB raster and tilescanning conversion process: the list ColWidth[i] for i ranging fromzero to num_tile_columns_minus1, inclusive, specifying the width of thei-th tile column in units of CTBs; the list RowHeight[j] for j rangingfrom zero to num_tile_rows_minus1, inclusive, specifying the height ofthe j-th tile row in units of CTBs; the list ColBd[i] for i ranging fromzero to num_tile_columns_minus1+1, inclusive, specifying the location ofthe i-th tile column boundary in units of CTBs; the list RowBd[j] for jranging from zero to num_tile_rows_minus1+1, inclusive, specifying thelocation of the j-th tile row boundary in units of CTBs; the listCtbAddrRsToTs[ctbAddrRs] for ctbAddrRs ranging from zero toPicSizeInCtbsY−1, inclusive, specifying the conversion from a CTBaddress in the CTB raster scan of a picture to a CTB address in the tilescan; the list CtbAddrTsToRs[ctbAddrTs] for ctbAddrTs ranging from zeroto PicSizeInCtbsY−1, inclusive, specifying the conversion from a CTBaddress in the tile scan to a CTB address in the CTB raster scan of apicture; the list Tileld[ctbAddrTs] for ctbAddrTs ranging from zero toPicSizeInCtbsY−1, inclusive, specifying the conversion from a CTBaddress in tile scan to a tile ID; the list NumCtuslnTile[tileldx] fortileldx ranging from zero to PicSizeInCtbsY−1, inclusive, specifying theconversion from a tile index to the number of CTUs in the tile; the listFirstCtbAddrTs[tileldx] for tileldx ranging from zero toNumTileslnPic−1, inclusive, specifying the conversion from a tile ID tothe CTB address in tile scan of the first CTB in the tile; the listColumnWidthInLumaSamples[i] for i ranging from zero tonum_tile_columns_minus1, inclusive, specifying the width of the i-thtile column in units of luma samples; and the listRowHeightInLumaSamples[j] for j ranging from zero tonum_tile_rows_minus1, inclusive, specifying the height of the j-th tilerow in units of luma samples. The values of ColumnWidthInLumaSamples[i]for i ranging from zero to num_tile_columns_minus1, inclusive, andRowHeightInLumaSamples[j] for j ranging from zero tonum_tile_rows_minus1, inclusive, shall all be greater than zero.

The loop_filter_across_tiles_enabled_flag equal to one specifies thatin-loop filtering operations may be performed across tile boundaries insub-pictures referring to the SPPS. Theloop_filter_across_tiles_enabled_flag equal to zero specifies thatin-loop filtering operations are not performed across tile boundaries insub-pictures referring to the SPPS. The in-loop filtering operationsinclude the deblocking filter, sample adaptive offset filter, andadaptive loop filter operations. When not present, the value ofloop_filter_across_tiles_enabled_flag is inferred to be equal to one.The loop_filter_across_subpic_enabled_flag equal to one specifies thatin-loop filtering operations may be performed across sub-pictureboundaries in sub-pictures referring to the SPPS. Theloop_filter_across_subpic_enabled_flag equal to zero specifies thatin-loop filtering operations are not performed across sub-pictureboundaries in sub-pictures referring to the SPPS. The in-loop filteringoperations include the deblocking filter, sample adaptive offset filter,and adaptive loop filter operations. When not present, the value ofloop_filter_across_subpic_enabled_flag is inferred to be equal to thevalue of loop_filter_across_tiles_enabled_flag.

The general tile group header syntax and semantics are as follows.

Descriptor tile_group_header( ) {   tile_group_subpic_id u(v)  tile_group_subpic_parameter_set_id u(v) . . . }

The value of the tile group header syntax elementtile_group_pic_parameter_set_id and tile_group_pic_order_cnt_lsb shallbe the same in all tile group headers of a coded picture. The value ofthe tile group header syntax element tile_group_subpic_id shall be thesame in all tile group headers of a coded sub-picture. Thetile_group_subpic_id identifies the sub-picture which the tile groupbelongs to. The length of tile_group_subpic_id is subpic_id_len_minus1+1bits. The tile_group_subpic_parameter_set_id specifies the value ofspps_subpic_parameter_set_id for the SPPS in use. The value oftile_group_spps_parameter_set_id shall be in the range of zero to sixtythree, inclusive.

The following variables are derived and override the respectivevariables derived from the active SPS:

-   -   PicWidthInLumaSamples=SubpicWidthInLumaSamples[tile_group_subpic_id]    -   PicHeightInLumaSamples=PicHeightInLumaSamples[tile_group_subpic_id]    -   SubPicRightBorderinPic=SubPicRightBorderInPic[tile_group_subpic_id]    -   SubPicBottomBorderInPic=SubPicBottomBorderInPic[tile_group_subpic_id]    -   PicWidthInCtbsY=SubPicWidthInCtbsY[tile_group_subpic_id]    -   PicHeightInCtbsY=SubPicHeightInCtbsY[tile_group_subpic_id]    -   PicSizeInCtbsY=SubPicSizeInCtbsY[tile_group_subpic_id]    -   PicWidthInMinCbsY=SubPicWidthInMinCbsY[tilegroup_subpic_id]    -   PicHeightInMinCbsY=SubPicHeightInMinCbsY [tile_group_subpic_id]    -   PicSizeInMinCbsY=SubPicSizeInMinCbsY[tile_group_subpic_id]    -   PicSizeInSamplesY=SubPicSizeInSamplesY[tile_group_subpic_id]    -   PicWidthInSamplesC=SubPicWidthInSamplesC [tile_group_subpic_id]    -   PicHeightInSamplesC=SubPicHeightInSamplesC[tile_group_subpic_id]

The coding tree unit syntax is as follows.

Descriptor coding_tree_unit( ) {   xCtb = ( CtbAddrInRs %PicWidthInCtbsY ) << CtbLog2SizeY + SubpictureXOffset   yCtb = (CtbAddrInRs / PicWidthInCtbsY ) << CtbLog2SizeY + SubpictureYOffset   .. . } dual_tree_implicit_qt_split( x0, y0, log2CbSize, cqtDepth ) {  if( log2CbSize > 6 ) {    x1 = x0 + ( 1 << ( log2CbSize − 1 ) )    y1= y0 + ( 1 << ( log2CbSize − 1 ) )    dual_tree_implicit_qt_split( x0,y0, log2CbSize − 1, cqtDepth + 1 )    if( x1 < SubPicRightBorderInPic )    dual_tree_implicit_qt_split( x1, y0, log2CbSize − 1, cqtDepth + 1 )   if( y1 < SubPicBottomBorderInPic )     dual_tree_implicit_qt_split(x0, y1, log2CbSize − 1, cqtDepth + 1 )    if( x1 <SubPicRightBorderInPic && y1 < SubPicBottomBorderInPic )    dual_tree_implicit_qt_split( x1, y1, log2CbSize − 1, cqtDepth + 1 )  } else {    coding_quadtree( x0, y0, log2CbSize, cqtDepth,DUAL_TREE_LUMA )    coding_quadtree( x0, y0, log2CbSize, cqtDepth,DUAL_TREE_CHROMA )   } }

The coding quadtree syntax and semantics are as follows.

Descrip- tor coding_quadtree( x0, y0, log2CbSize, cqtDepth, treeType ) { minQtSize = ( treeType = = DUAL_TREE_CHROMA ) ? MinQtSizeC : MinQtSizeY maxBtSize = ( treeType = = DUAL_TREE_CHROMA ) ? MaxBtSizeC : MaxBtSizeY if( ( ( ( x0 + ( 1 << log2CbSize ) <= PicWidthInLumaSamples ) ? 1 : 0) + ( ( y0 + ( 1 << log2CbSize ) <= PicHeightInLumaSamples ) ? 1 : 0 ) +( ( ( 1 << log2CbSize ) <= maxBtSize ) ? 1 : 0 ) ) >= 2 && ( 1 <<log2CbSize ) > minQtSize )    qt_split_cu_flag[ x0 ][ y0 ] ae(v)   if(cu_qp_delta_enabled_flag && cqtDepth <= diff_cu_qp_delta_depth ) {   IsCuQpDeltaCoded = 0    CuQpDeltaVal = 0    CuQgTopLeftX = x0   CuQgTopLeftY = y0   }   if( qt_split_cu_flag[ x0 ][ y0 ] ) {    x1 =x0 + ( 1 << ( log2CbSize − 1 ) )    y1 = y0 + ( 1 << ( log2CbSize − 1 ))   coding_quadtree( x0, y0, log2CbSize − 1, cqtDepth + 1,   treeType )   if( x1 < SubPicRightBorderInPic )   coding_quadtree( x1, y0,log2CbSize − 1, cqtDepth + 1,   treeType )    if( y1 <SubPicBottomBorderInPic )   coding_quadtree( x0, y1, log2CbSize − 1,cqtDepth + 1,   treeType )    if( x1 < SubPicRightBorderInPic && y1 <SubPicBottomBorderInPic )   coding_quadtree( x1, y1, log2CbSize − 1,cqtDepth + 1,   treeType )   } else   multi_type_tree( x0, y0, 1 <<log2CbSize, 1 << log2CbSize, cqtDepth, 0, 0, 0, treeType ) }

The qt_split_cu_flag[x0][y0] specifies whether a coding unit is splitinto coding units with half horizontal and vertical size. The arrayindices x0, y0 specify the location (x0, y0) of the top-left luma sampleof the considered coding block relative to the top-left luma sample ofthe picture. When qt_split_cu_flag[x0][y0] is not present, the followingapplies: If one or more of the following conditions are true, the valueof qt_split_cu_flag[x0][y0] is inferred to be equal to one. x0+(1<<log2CbSize) is greater than SubPicRightBorderinPic and (1<<log 2CbSize) isgreater than MaxBtSizeC if treeType is equal to DUAL_TREE_CHROMA orgreater than MaxBtSizeY otherwise. y0+(1<<log 2CbSize) is greater thanSubPicBottomBorderinPic and (1<<log 2CbSize) is greater than MaxBtSizeCif treeType is equal to DUAL_TREE_CHROMA or greater than MaxBtSizeYotherwise.

Otherwise, if all of the following conditions are true, the value ofqt_split_cu_flag[x0][y0] is inferred to be equal to 1: x0+(1<<log2CbSize) is greater than SubPicRightBorderinPic, y0+(1<<log 2CbSize) isgreater than SubPicBottomBorderInPic, and (1<<log 2CbSize) is greaterthan MinQtSizeC if treeType is equal to DUAL_TREE_CHROMA or greater thanMinQtSizeY otherwise. Otherwise, the value of qt_split_cu_flag[x0][y0]is inferred to be equal to zero.

The multi-type tree syntax and semantics are as follows.

De- scrip- tor multi_type_tree( x0, y0, cbWidth, cbHeight, cqtDepth,mttDepth, depthOffset, partIdx, treeType ) {   if( ( allowSplitBtVer | |allowSplitBtHor | | allowSplitTtVer | | allowSplitTtHor ) &&    ( x0 +cbWidth <= SubPicRightBorderInPic ) &&    (y0 + cbHeight <=SubPicBottomBorderInPic ) )    mtt_split_cu_flag ae(v)   if(cu_qp_delta_enabled_flag && ( cqtDepth + mttDepth ) <=diff_cu_qp_delta_depth ) {    IsCuQpDeltaCoded = 0    CuQpDeltaVal = 0   CuQgTopLeftX = x0    CuQgTopLeftY = y0   }   if( mtt_split_cu_flag ){    if( ( allowSplitBtHor | | allowSplitTtHor ) &&     (allowSplitBtVer | | allowSplitTtVer ) )     mtt_split_cu_vertical_flagae(v)    if( ( allowSplitBtVer && allowSplitTtVer &&mtt_split_cu_vertical_flag ) | |     ( allowSplitBtHor &&allowSplitTtHor && !mtt_split_cu_vertical_flag ) )    mtt_split_cu_binary_flag ae(v)    if( MttSplitMode[ x0 ][ y0 ][mttDepth ] = = SPLIT_BT_VER ) {   depthOffset += ( x0 + cbWidth >  SubPicRightBorderInPic ) ? 1 : 0     x1 = x0 + ( cbWidth / 2 )    multi_type_tree( x0, y0, cbWidth / 2, cbHeight,     cqtDepth,mttDepth + 1, depthOffset, 0, treeType )     if( x1 <SubPicRightBorderInPic )   multi_type_tree( x1, y0, cbWidth / 2,cbHeightY,   cqtDepth, mttDepth + 1, depthOffset, 1, treeType )   } elseif( MttSplitMode[ x0 ][ y0 ][ mttDepth ] = = SPLIT_BT_HOR ) {  depthOffset += (y0 + cbHeight >   SubPicBottomBorderInPic ) ? 1 : 0    y1 = y0 + ( cbHeight / 2 )     multi_type_tree( x0, y0, cbWidth,cbHeight / 2,   cqtDepth, mttDepth + 1, depthOffset, 0, treeType )    if( y1 < SubPicBottomBorderInPic )      multi_type_tree( x0, y1,cbWidth, cbHeight / 2,   cqtDepth, mttDepth + 1, depthOffset, 1,treeType )    } else if( MttSplitMode[ x0 ][ y0 ][ mttDepth ] = =SPLIT_TT_VER ) {     x1 = x0 + ( cbWidth / 4 )     x2 = x0 + ( 3 *cbWidth / 4 )     multi_type_tree( x0, y0, cbWidth / 4, cbHeight,  cqtDepth, mttDepth + 1, depthOffset, 0, treeType )    multi_type_tree( x1, y0, cbWidth / 2, cbHeight,   cqtDepth,mttDepth + 1, depthOffset, 1, treeType )     multi_type_tree( x2, y0,cbWidth / 4, cbHeight,   cqtDepth, mttDepth + 1, depthOffset, 2,treeType )    } else { /* SPLIT_TT_HOR */     y1 = y0 + ( cbHeight / 4 )    y2 = y0 + ( 3 * cbHeight / 4 )     multi_type_tree( x0, y0, cbWidth,cbHeight / 4,   cqtDepth, mttDepth + 1, depthOffset, 0, treeType )    multi_type_tree( x0, y1, cbWidth, cbHeight / 2,   cqtDepth,mttDepth + 1, depthOffset, 1, treeType )     multi_type_tree( x0, y2,cbWidth, cbHeight / 4,   cqtDepth, mttDepth + 1, depthOffset, 2 ,treeType)    }   } else    coding_unit( x0, y0, cbWidth, cbHeight,treeType ) }

The mtt_split_cu_flag equal to zero specifies that a coding unit is notsplit. The mtt_split_cu_flag equal to one specifies that a coding unitis split into two coding units using a binary split or into three codingunits using a ternary split as indicated by the syntax elementmtt_split_cu_binary_flag. The binary or ternary split can be eithervertical or horizontal as indicated by the syntax elementmtt_split_cu_vertical_flag. When mtt_split_cu_flag is not present, thevalue of mtt_split_cu_flag is inferred as follows. If one or more of thefollowing conditions are true, the value of mtt_split_cu_flag isinferred to be equal to 1: x0+cbWidth is greater thanSubPicRightBorderinPic, and y0+cbHeight is greater thanSubPicBottomBorderinPic. Otherwise, the value of mtt_split_cu_flag isinferred to be equal to zero.

The derivation process for temporal luma motion vector prediction is asfollows. The outputs of this process are: the motion vector predictionmvLXCol in 1/16 fractional-sample accuracy, and the availability flagavailableFlagLXCol. The variable currCb specifies the current lumacoding block at luma location (xCb, yCb). The variables mvLXCol andavailableFlagLXCol are derived as follows. Iftile_group_temporal_mvp_enabled_flag is equal to zero, or if thereference picture is the current picture, both components of mvLXCol areset equal to zero and availableFlagLXCol is set equal to zero. Otherwise(tile_group_temporal_mvp_enabled_flag is equal to one and the referencepicture is not the current picture), the following ordered steps apply.The bottom right collocated motion vector is derived as follows:

xColBr=xCb+cbWidth  (8-355)

yColBr=yCb+cbHeight  (8-356)

If yCb>>CtbLog 2SizeY is equal to yColBr>>CtbLog 2SizeY, yColBr is lessthan SubPicBottomBorderinPic and xColBr is less thanSubPicRightBorderinPic, the following applies. The variable colCbspecifies the luma coding block covering the modified location given by((xColBr>>3)<<3, (yColBr>>3)<<3) inside the collocated picture specifiedby ColPic. The luma location (xColCb, yColCb) is set equal to thetop-left sample of the collocated luma coding block specified by colCbrelative to the top-left luma sample of the collocated picture specifiedby ColPic. The derivation process for collocated motion vectors isinvoked with currCb, colCb, (xColCb, yColCb), refIdxLX and sbFlag setequal to zero as inputs, and the output is assigned to mvLXCol andavailableFlagLXCol. Otherwise, both components of mvLXCol are set equalto zero and availableFlagLXCol is set equal to zero.

The derivation process for temporal triangle merging candidates is asfollows. The variables mvLXColC0, mvLXColC1, availableFlagLXColC0 andavailableFlagLXColC1 are derived as follows. Iftile_group_temporal_mvp_enabled_flag is equal to zero, both componentsof mvLXColC0 and mvLXColC1 are set equal to zero andavailableFlagLXColC0 and availableFlagLXColC1 are set equal to zero.Otherwise (tile_group_temporal_mvp_enabled_flag is equal to 1), thefollowing ordered steps apply. The bottom right collocated motion vectormvLXColC0 is derived as follows:

xColBr=xCb+cbWidth  (8-392)

yColBr=yCb+cbHeight  (8-393)

If yCb>>CtbLog 2SizeY is equal to yColBr>>CtbLog 2SizeY, yColBr is lessthan SubPicBottomBorderinPic and xColBr is less thanSubPicRightBorderinPic, the following applies. The variable colCbspecifies the luma coding block covering the modified location given by((xColBr>>3)<<3, (yColBr>>3)<<3) inside the collocated picture specifiedby ColPic. The luma location (xColCb, yColCb) is set equal to thetop-left sample of the collocated luma coding block specified by colCbrelative to the top-left luma sample of the collocated picture specifiedby ColPic. The derivation process for collocated motion vectors isinvoked with currCb, colCb, (xColCb, yColCb), refIdxLXC0 and sbFlag setequal to zero as inputs, and the output is assigned to mvLXColC0 andavailableFlagLXColC0. Otherwise, both components of mvLXColC0 are setequal to zero and availableFlagLXColC0 is set equal to zero.

The derivation process for constructed affine control point motionvector merging candidates is as follows. The fourth (collocatedbottom-right) control point motion vector cpMvLXCorner[3], referenceindex refIdxLXCorner[3], prediction list utilization flagpredFlagLXCorner[3] and the availability flag availableFlagCorner[3]with X being 0 and 1 are derived as follows. The reference indices forthe temporal merging candidate, refIdxLXCorner[3], with X being zero orone, are set equal to zero. The variables mvLXCol andavailableFlagLXCol, with X being zero or one, are derived as follows. Iftile_group_temporal_mvp_enabled_flag is equal to zero, both componentsof mvLXCol are set equal to zero and availableFlagLXCol is set equal tozero. Otherwise (tile_group_temporal_mvp_enabled_flag is equal to one),the following applies:

xColBr=xCb+cbWidth  (8-566)

yColBr=yCb+cbHeight  (8-567)

If yCb>>CtbLog 2SizeY is equal to yColBr>>CtbLog 2SizeY, yColBr is lessthan SubPicBottomBorderinPic and xColBr is less thanSubPicRightBorderinPic, the following applies. The variable colCbspecifies the luma coding block covering the modified location given by((xColBr>>3)<<3, (yColBr>>3)<<3) inside the collocated picture specifiedby ColPic. The luma location (xColCb, yColCb) is set equal to thetop-left sample of the collocated luma coding block specified by colCbrelative to the top-left luma sample of the collocated picture specifiedby ColPic. The derivation process for collocated motion vectors isinvoked with currCb, colCb, (xColCb, yColCb), refIdxLX and sbFlag setequal to zero as inputs, and the output is assigned to mvLXCol andavailableFlagLXCol. Otherwise, both components of mvLXCol are set equalto 0 and availableFlagLXCol is set equal to zero. Replace alloccurrences of pic_width_in_luma_samples with PicWidthInLumaSamples.Replace all occurrences of pic_height_in_luma_samples withPicHeightInLumaSamples.

In a second example embodiment, the sequence parameter set RBSP syntaxand semantics are as follows.

Descriptor seq_parameter_set_rbsp( ) {   sps_seq_parameter_set_id ue(v)  pic_width_in_luma_samples ue(v)   pic_height_in_luma_samples ue(v)  num_subpic_minus1 ue(v)   subpic_id_len_minus1 ue(v)   for ( i = 0; i<= num_subpic_minus1; i++ ) {    subpic_id[ i ] u(v)    if(num_subpic_minus1 > 0 ) {     subpic_level_idc[ i ] u(8)    subpic_x_offset[ i ] ue(v)     subpic_y_offset[ i ] ue(v)    subpic_width_in_luma_samples[ i ] ue(v)    subpic_height_in_luma_samples[ i ] ue(v)    }   } . . . }

The subpic_id_len_minus1 plus one specifies the number of bits used torepresent the syntax element subpic_id[i] in SPS, spps_subpic_id in SPPSreferring to the SPS, and tile_group_subpic_id in tile group headersreferring to the SPS. The value of subpic_id_len_minus1 shall be in therange of Ceil(Log 2(num_subpic_minus1+3) to eight, inclusive. It is arequirement of bitstream conformance that there shall be no overlapamong sub-picture[i] for i from 0 to num_subpic_minus1, inclusive. Eachsub-picture may be a temporal motion constrained sub-picture.

The general tile group header semantics are as follows. Thetile_group_subpic_id identifies the sub-picture which the tile groupbelongs to. The length of tile_group_subpic_id is subpic_id_len_minus1+1bits. The tile_group_subpic_id equal to one indicates the tile groupdoes not belong to any sub-picture.

In a third example embodiment, the NAL unit header syntax and semanticsare as follows.

Descriptor nal_unit_header( ) {  forbidden_zero_bit f(1)  nal_unit_typeu(5)  nuh_temporal_id_plus1 u(3)  nuh_subpicture_id_len u(4) nuh_reserved_zero_4bits u(3) }

The nuh_subpicture_id_len specifies the number of bits used to representthe syntax element specifying sub-picture ID. When the value ofnuh_subpicture_id_len is greater than zero, the firstnuh_subpicture_id_len-th bits in after nuh_reserved_zero_4 bitsspecifies the ID of the sub-picture which the payload of the NAL unitbelongs to. When nuh_subpicture_id_len is greater than zero, the valueof nuh_subpicture_id_len shall be equal to the value ofsubpic_id_len_minus1 in the active SPS. The value ofnuh_subpicture_id_len for non-VCL NAL units is constrained as follows.If nal_unit_type is equal to SPS_NUT or PPS_NUT, nuh_subpicture_id_lenshall be equal to zero. The nuh_reserved_zero_3 bits shall be equal to‘000’. Decoders shall ignore (e.g., remove from the bitstream anddiscard) NAL units with values of nuh_reserved_zero_3 bits not equal to‘000’.

In a fourth example embodiment, sub-picture nesting syntax is asfollows.

Descriptor sub-picture_nesting( payloadSize ) {  all_sub_pictures_flagu(1)  if( !all_sub_pictures_flag ) {   nesting_num_sub_pictures_minus1ue(v)   for( i = 0; i <= nesting_num_sub_pictures_minus1; i++ )   nesting_sub_picture_id[ i ] u(v)  }  while( !byte_aligned( ) )  sub_picture_nesting_zero_bit /* equal to 0 */ u(1)  do   sei_message()  while( more_rbsp_data( ) ) }

The all_sub_pictures_flag equal to one specifies that the nested SEImessages apply to all the sub-pictures. all_sub_pictures_flag equal toone specifies that the sub-pictures to which the nested SEI messagesapply are explicitly signaled by the subsequent syntax elements. Thenesting_num_sub_pictures_minus1 plus 1 specifies the number ofsub-pictures to which the nested SEI messages apply. Thenesting_sub_picture_id[i] indicates the sub-picture ID of the i-thsub-picture to which the nested SEI messages apply. Thenesting_sub_picture_id[i] syntax element is represented by Ceil(Log2(nesting_num_sub_pictures_minus1+1)) bits. Thesub_picture_nesting_zero_bit shall be equal to zero.

FIG. 9 is a schematic diagram of an example video coding device 900. Thevideo coding device 900 is suitable for implementing the disclosedexamples/embodiments as described herein. The video coding device 900comprises downstream ports 920, upstream ports 950, and/or transceiverunits (Tx/Rx) 910, including transmitters and/or receivers forcommunicating data upstream and/or downstream over a network. The videocoding device 900 also includes a processor 930 including a logic unitand/or central processing unit (CPU) to process the data and a memory932 for storing the data. The video coding device 900 may also compriseelectrical, optical-to-electrical (OE) components, electrical-to-optical(EO) components, and/or wireless communication components coupled to theupstream ports 950 and/or downstream ports 920 for communication of datavia electrical, optical, or wireless communication networks. The videocoding device 900 may also include input and/or output (I/O) devices 960for communicating data to and from a user. The I/O devices 960 mayinclude output devices such as a display for displaying video data,speakers for outputting audio data, etc. The I/O devices 960 may alsoinclude input devices, such as a keyboard, mouse, trackball, etc.,and/or corresponding interfaces for interacting with such outputdevices.

The processor 930 is implemented by hardware and software. The processor930 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), field-programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), and digital signalprocessors (DSPs). The processor 930 is in communication with thedownstream ports 920, Tx/Rx 910, upstream ports 950, and memory 932. Theprocessor 930 comprises a coding module 914. The coding module 914implements the disclosed embodiments described above, such as methods100, 1000, 1100, and/or mechanism 700, which may employ a bitstream 500,a picture 600, and/or a picture 800. The coding module 914 may alsoimplement any other method/mechanism described herein. Further, thecoding module 914 may implement a codec system 200, an encoder 300,and/or a decoder 400. For example, the coding module 914 may be employedto signal and/or obtain sub-picture locations and sizes in an SPS. Inanother example, the coding module 914 may constrain sub-picture widthsand sub-picture heights to be multiples of CTU size unless suchsub-pictures are positioned at the right border of the picture or thebottom border of the picture, respectively. In another example, thecoding module 914 may constrain sub-pictures to cover a picture withoutgap or overlap. In another example, the coding module 914 may beemployed to signal and/or obtain data indicating some sub-pictures aretemporal motion constrained sub-pictures and other sub-pictures are not.In another example, the coding module 914 may signal a complete set ofsub-picture IDs in the SPS and include a sub-picture ID in each sliceheader to indicate the sub-picture that contains corresponding slices.In another example, the coding module 914 may signal levels for eachsub-picture. As such, the coding module 914 causes the video codingdevice 900 to provide additional functionality, avoid certain processingto reduce processing overhead, and/or increase coding efficiency whenpartitioning and coding video data. Accordingly, the coding module 914improves the functionality of the video coding device 900 as well asaddresses problems that are specific to the video coding arts. Further,the coding module 914 effects a transformation of the video codingdevice 900 to a different state. Alternatively, the coding module 914can be implemented as instructions stored in the memory 932 and executedby the processor 930 (e.g., as a computer program product stored on anon-transitory medium).

The memory 932 comprises one or more memory types such as disks, tapedrives, solid-state drives, read only memory (ROM), random access memory(RAM), flash memory, ternary content-addressable memory (TCAM), staticrandom-access memory (SRAM), etc. The memory 932 may be used as anover-flow data storage device, to store programs when such programs areselected for execution, and to store instructions and data that are readduring program execution.

FIG. 10 is a flowchart of an example method 1000 of encoding abitstream, such as bitstream 500 and/or sub-bitstream 501, ofsub-pictures, such as sub-pictures 522, 523, 622, 722, and/or 822, withadaptive size constraints. Method 1000 may be employed by an encoder,such as a codec system 200, an encoder 300, and/or a video coding device900 when performing method 100.

Method 1000 may begin when an encoder receives a video sequenceincluding a plurality of pictures and determines to encode that videosequence into a bitstream, for example based on user input. The videosequence is partitioned into pictures/images/frames for furtherpartitioning prior to encoding. At step 1001, a picture is partitionedinto a plurality of sub-pictures. An adaptive size constraint is appliedwhen partitioning the sub-pictures. The sub-pictures each include asub-picture width and a sub-picture height. When a current sub-pictureincludes a right border that does not coincide with a right border ofthe picture, the sub-picture width of the current sub-picture isconstrained to be an integer multiple of a CTU (e.g., sub-pictures 822other than 822 b). Accordingly, at least one of the sub-pictures (e.g.,sub-pictures 822 b) may include a sub-picture width that is not aninteger multiple of the CTU size when the each sub-picture includes aright border that coincides with the right border of the picture.Further, when a current sub-picture includes a bottom border that doesnot coincide with a bottom border of the picture, the sub-picture heightof the current sub-picture is constrained to be an integer multiple of aCTU (e.g., sub-pictures 822 other than 822 c). Accordingly, at least oneof the sub-pictures (e.g., sub-pictures 822 c) may include a sub-pictureheight that is not an integer multiple of the CTU size when the eachsub-picture includes a bottom border that coincides with the bottomborder of the picture. This adaptive size constraint allows sub-picturesto be partitioned from a picture that includes a picture width that isnot an integer multiple of the CTU size and/or a picture height that isnot an integer multiple of the CTU size. The CTU size may be measured inunits of luma samples.

At step 1003, the one or more of the sub-pictures are encoded into abitstream. The bitstream is stored for communication toward a decoder atstep 1005. The bitstream may then be transmitted toward the decoder asdesired. In some examples, a sub-bitstream may be extracted from theencoded bitstream. In such a case, the transmitted bitstream is asub-bitstream. In other examples, the encoded bitstream may betransmitted for sub-bitstream extraction at the decoder. In yet otherexamples, the encoded bitstream may be decoded and displayed withoutsub-bitstream extraction. In any of these examples, the adaptive sizeconstraint allows sub-pictures to be partitioned from a picture with aheight or width that is not a multiple of CTU size, and hence increasesthe functionality of the encoder.

FIG. 11 is a flowchart of an example method 1100 of decoding abitstream, such as bitstream 500 and/or sub-bitstream 501, ofsub-pictures, such as sub-pictures 522, 523, 622, 722, and/or 822, withadaptive size constraints. Method 1100 may be employed by a decoder,such as a codec system 200, a decoder 400, and/or a video coding device900 when performing method 100. For example, method 1100 may be appliedto decode a bitstream created as a result of method 1000.

Method 1100 may begin when a decoder begins receiving a bitstreamcontaining sub-pictures. The bitstream may include a complete videosequence or the bitstream may be a sub-bitstream containing a reducedset of sub-pictures for separate extraction. At step 1101, a bitstreamis received. The bitstream comprises one or more sub-picturespartitioned from a picture according to an adaptive size constraint. Thesub-pictures each include a sub-picture width and a sub-picture height.When a current sub-picture includes a right border that does notcoincide with a right border of the picture, the sub-picture width ofthe current sub-picture is constrained to be an integer multiple of aCTU (e.g., sub-pictures 822 other than 822 b). Accordingly, at least oneof the sub-pictures (e.g., sub-pictures 822 b) may include a sub-picturewidth that is not an integer multiple of the CTU size when the eachsub-picture includes a right border that coincides with the right borderof the picture. Further, when a current sub-picture includes a bottomborder that does not coincide with a bottom border of the picture, thesub-picture height of the current sub-picture is constrained to be aninteger multiple of a CTU (e.g., sub-pictures 822 other than 822 c).Accordingly, at least one of the sub-pictures (e.g., sub-pictures 822 c)may include a sub-picture height that is not an integer multiple of theCTU size when the each sub-picture includes a bottom border thatcoincides with the bottom border of the picture. This adaptive sizeconstraint allows sub-pictures to be partitioned from a picture thatincludes a picture width that is not an integer multiple of the CTU sizeand/or a picture height that is not an integer multiple of the CTU size.The CTU size may be measured in units of luma samples.

At step 1103, the bitstream is parsed to obtain the one or moresub-pictures. At step 1105, the one or more sub-pictures are decoded tocreate a video sequence. The video sequence can then be forwarded fordisplay. Hence, the adaptive size constraint allows sub-pictures to bepartitioned from a picture with a height or width that is not a multipleof CTU size. Accordingly, the decoder can employ sub-picture basedfunctionality, such as separate sub-picture extraction and/or display,on a picture with a height or width that is not a multiple of CTU size.As such, the application of adaptive size constraint increases thefunctionality of the decoder.

FIG. 12 is a schematic diagram of an example system 1200 for signaling abitstream, such as bitstream 500 and/or sub-bitstream 501, ofsub-pictures, such as sub-pictures 522, 523, 622, 722, and/or 822, withadaptive size constraints. System 1200 may be implemented by an encoderand a decoder such as a codec system 200, an encoder 300, a decoder 400,and/or a video coding device 900. Further, system 1200 may be employedwhen implementing method 100, 1000, and/or 1100.

The system 1200 includes a video encoder 1202. The video encoder 1202comprises a partitioning module 1201 for partitioning a picture into aplurality of sub-pictures such that each sub-picture includes asub-picture width that is an integer multiple of a CTU size when theeach sub-picture includes a right border that does not coincide with aright border of the picture. The video encoder 1202 further comprises anencoding module 1203 for encoding one or more of the sub-pictures into abitstream. The video encoder 1202 further comprises a storing module1205 for storing the bitstream for communication toward a decoder. Thevideo encoder 1202 further comprises a transmitting module 1207 fortransmitting the bitstream including the sub-pictures toward thedecoder. The video encoder 1202 may be further configured to perform anyof the steps of method 1000.

The system 1200 also includes a video decoder 1210. The video decoder1210 comprises a receiving module 1211 for receiving a bitstreamcomprising one or more sub-pictures partitioned from a picture such thateach sub-picture includes a sub-picture width that is an integermultiple of a coding tree unit (CTU) size when the each sub-pictureincludes a right border that does not coincide with a right border ofthe picture. The video decoder 1210 further comprises a parsing module1213 for parsing the bitstream to obtain the one or more sub-pictures.The video decoder 1210 further comprises a decoding module 1215 fordecoding the one or more sub-pictures to create a video sequence. Thevideo decoder 1210 further comprises a forwarding module 1217 forforwarding the video sequence for display. The video decoder 1210 may befurther configured to perform any of the steps of method 1100.

A first component is directly coupled to a second component when thereare no intervening components, except for a line, a trace, or anothermedium between the first component and the second component. The firstcomponent is indirectly coupled to the second component when there areintervening components other than a line, a trace, or another mediumbetween the first component and the second component. The term “coupled”and its variants include both directly coupled and indirectly coupled.The use of the term “about” means a range including ±10% of thesubsequent number unless otherwise stated.

It should also be understood that the steps of the exemplary methods setforth herein are not necessarily required to be performed in the orderdescribed, and the order of the steps of such methods should beunderstood to be merely exemplary. Likewise, additional steps may beincluded in such methods, and certain steps may be omitted or combined,in methods consistent with various embodiments of the presentdisclosure.

While several embodiments have been provided in the present disclosure,it may be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, components, techniques, ormethods without departing from the scope of the present disclosure.Other examples of changes, substitutions, and alterations areascertainable by one skilled in the art and may be made withoutdeparting from the spirit and scope disclosed herein.

What is claimed is:
 1. A method implemented by an encoder, the method comprising: generating a bitstream comprising a sequence parameter set (SPS) and one or more sub-pictures partitioned from a picture such that a first sub-picture includes more than one slice and includes an incomplete coding tree unit (CTU) when the first sub-picture includes a right boundary that coincides with the right boundary of the picture, wherein the SPS comprises a sub-picture identifier (ID), a sub-picture size, and a sub-picture location for each of the one or more sub-pictures; and transmitting the bitstream toward a decoder.
 2. The method of claim 1, wherein a second sub-picture comprises a sub-picture height that includes an integer number of complete CTUs when the second sub-picture includes a bottom boundary that does not coincide with a bottom boundary of the picture.
 3. The method of claim 1, wherein a third sub-picture comprises a sub-picture width that includes an integer number of complete CTUs when the third sub-picture includes a right boundary that does not coincide with a right boundary of the picture.
 4. The method of claim 1, wherein a fourth sub-picture comprises a sub-picture height that includes an incomplete CTU when the fourth sub-picture includes a bottom boundary that coincides with the bottom boundary of the picture.
 5. A method implemented by an encoder, the method comprising: generating a bitstream comprising a sequence parameter set (SPS) and a picture partitioned into sub-pictures, wherein at least one sub-picture includes more than one slice and includes an incomplete coding tree unit (CTU) when the at least one sub-picture includes a right boundary that coincides with the right boundary of the picture, wherein the SPS comprises a sub-picture identifier (ID), a sub-picture size, and a sub-picture location for each of the one or more sub-pictures; and transmitting the bitstream toward a decoder.
 6. The method of claim 5, wherein each sub-picture includes a sub-picture height that is an integer multiple of a CTU size when each sub-picture includes a bottom boundary that does not coincide with a bottom boundary of the picture.
 7. The method of claim 5, wherein each sub-picture includes a sub-picture width that is an integer multiple of a CTU size when each sub-picture includes a right boundary that does not coincide with a right boundary of the picture.
 8. The method of claim 5, wherein at least one of the sub-pictures includes a sub-picture height that is not an integer multiple of a CTU size when each sub-picture includes a bottom boundary that coincides with the bottom boundary of the picture.
 9. The method of claim 5, wherein the picture includes a picture width that is not an integer multiple of a CTU size.
 10. The method of claim 5, wherein the picture includes a picture height that is not an integer multiple of a CTU size.
 11. The method of claim 5, wherein a CTU size is measured in units of luma samples.
 12. An encoder, comprising: a memory storing instructions; and one or more processors coupled to the memory, wherein the one or more processors are configured to execute the instructions to cause the encoder to: generate a bitstream comprising a sequence parameter set (SPS) and a picture partitioned into sub-pictures, wherein at least one sub-picture includes more than one slice and includes an incomplete coding tree unit (CTU) when the at least one sub-picture includes a right boundary that coincides with the right boundary of the picture, wherein the SPS comprises a sub-picture identifier (ID), a sub-picture size, and a sub-picture location for each of the one or more sub-pictures; and transmit the bitstream toward a decoder.
 13. The encoder of claim 12, wherein each sub-picture includes a sub-picture height that is an integer multiple of a CTU size when each sub-picture includes a bottom boundary that does not coincide with a bottom boundary of the picture.
 14. The encoder of claim 12, wherein each sub-picture includes a sub-picture width that is an integer multiple of a CTU size when each sub-picture includes a right boundary that does not coincide with a right boundary of the picture.
 15. The encoder of claim 12, wherein at least one of the sub-pictures includes a sub-picture height that is not an integer multiple of a CTU size when each sub-picture includes a bottom boundary that coincides with the bottom boundary of the picture.
 16. The encoder of claim 12, wherein the picture includes a picture width that is not an integer multiple of a CTU size.
 17. The encoder of claim 12, wherein the picture includes a picture height that is not an integer multiple of a CTU size.
 18. The encoder of claim 12, wherein a CTU size is measured in units of luma samples.
 19. A non-transitory computer-readable recording medium storing a bitstream generated by a method implemented by an encoder, wherein the method comprises: generating a bitstream comprising a sequence parameter set (SPS) and a picture partitioned into sub-pictures, wherein at least one sub-picture includes more than one slice and includes an incomplete coding tree unit (CTU) when the at least one sub-picture includes a right boundary that coincides with the right boundary of the picture, wherein the SPS comprises a sub-picture identifier (ID), a sub-picture size, and a sub-picture location for each of the one or more sub-pictures; and transmitting the bitstream toward a decoder.
 20. The non-transitory computer-readable recording medium of claim 19, wherein a second sub-picture comprises a sub-picture height that includes an integer number of complete CTUs when the second sub-picture includes a bottom boundary that does not coincide with a bottom boundary of the picture.
 21. The non-transitory computer-readable recording medium of claim 19, wherein a third sub-picture comprises a sub-picture width that includes an integer number of complete CTUs when the third sub-picture includes a right boundary that does not coincide with a right boundary of the picture.
 22. The non-transitory computer-readable recording medium of claim 19, wherein a fourth sub-picture comprises a sub-picture height that includes an incomplete CTU when the fourth sub-picture includes a bottom boundary that coincides with the bottom boundary of the picture. 